opinion: SKIPPER v. SOUTH CAROLINA
  No. 84-6859.
  Argued February 24, 1986
  Decided April 29, 1986
  White, J., delivered the opinion of the Court, in which Brennan, Marshall, Blackmun, Stevens, and O’Connor, JJ., joined. Powell, J., filed an opinion concurring in the judgment, in which Burger, C. J., and Rehnquist, J., joined, post, p. 9.
  David I. Bruck, by appointment of the Court, 474 U. S. 942, argued the cause and filed briefs for petitioner.
  Harold M. Coombs, Jr., Assistant Attorney General of South Carolina, argued the cause for respondent. With him on the brief was T. Travis Medlock, Attorney General.
  A brief of amici curiae was filed for the State of Alabama et al. by David Crump, Charles A. Graddick, Attorney General of Alabama, Steve Clark, Attorney General of Arkansas, James J. Kelly, Chief State’s Attorney of Connecticut, Jim Smith, Attorney General of Florida, James T. Jones, Attorney General of Idaho, William L. Webster, Attorney General of Missouri, LeRoy S. Zimmerman, Attorney General of Pennsylvania, Gerald L. Baliles, Attorney General of Virginia, Kenneth 0. Eikenberry, Attorney General of Washington, and Archie G. McClintock, Attorney General of Wyoming.
  Justice White
  delivered the opinion of the Court.
  Petitioner Ronald Skipper was convicted in a South Carolina trial court of capital murder and rape. The State sought the death penalty, and a separate sentencing hearing was held before the trial jury under S. C. Code § 16-3-20 (1985), which provides for a bifurcated trial and jury sentencing in capital cases. Following introduction by the State of evidence in aggravation of the offense (principally evidence of petitioner’s history of sexually assaultive behavior), petitioner presented as mitigating evidence his own testimony and that of his former wife, his mother, his sister, and his grandmother. This testimony, for the most part, concerned the difficult circumstances of his upbringing. Petitioner and his former wife, however, both testified briefly that petitioner had conducted himself well during the Tk months he spent in jail between his arrest and trial. Petitioner also testified that during a prior period of incarceration he had earned the equivalent of a high school diploma and that, if sentenced to life imprisonment rather than to death, he would behave himself in prison and would attempt to work so that he could contribute money to the support of his family.
  Petitioner also sought to introduce testimony of two jailers and one “regular visitor” to the jail to the effect that petitioner had “made a good adjustment” during his time spent in jail. The trial court, however, ruled that under the South Carolina Supreme Court’s decision in State v. Koon, 278 S. C. 528, 298 S. E. 2d 769 (1982) (Koon I), such evidence would be irrelevant and hence inadmissible. The decision in Koon I, the judge stated, stood for the rule that “whether [petitioner] can adjust or not adjust” was “not an issue in this case.” App. 11.
  After hearing closing arguments — during the course of which the prosecutor contended that petitioner would pose disciplinary problems if sentenced to prison and would likely rape other prisoners, id., at 13-14 — the jury sentenced petitioner to death. On appeal, petitioner contended that the trial court had committed constitutional error in excluding the testimony of the jailers and the visitor: the testimony of these witnesses, petitioner argued, would have constituted relevant mitigating evidence, and exclusion of such evidence was improper under this Court’s decisions in Lockett v. Ohio, 438 U. S. 586 (1978), and Eddings v. Oklahoma, 455 U. S. 104 (1982). The Supreme Court of South Carolina rejected petitioner’s contention, stating:
  “The trial judge properly refused to admit evidence of [petitioner’s] future adaptability to prison life. State v. Koon, supra. However, evidence of his past adaptability was admitted through testimony of his former wife, his mother and his own testimony. This contention is without merit.” 285 S. C. 42, 48, 328 S. E. 2d 58, 61-62 (1985).
  We granted certiorari, 474 U. S. 900 (1985), to consider petitioner’s claim that the South Carolina Supreme Court’s decision is inconsistent with this Court’s decisions in Lockett and Eddings, and we now reverse.
  There is no disputing that this Court’s decision in Eddings requires that in capital cases “ ‘the sentencer . . . not be precluded from considering, as a mitigating factor, any aspect of a defendant’s character or record and any of the circumstances of the offense that the defendant proffers as a basis for a sentence less than death.’” Eddings, supra, at 110 (quoting Lockett, supra, at 604 (plurality opinion of Burger, C. J.)) (emphasis in original). Equally clear is the corollary rule that the sentencer may not refuse to consider or be precluded from considering “any relevant mitigating evidence.” 455 U. S., at 114. These rules are now well established, and the State does not question them.
  Accordingly, the only question before us is whether the exclusion from the sentencing hearing of the testimony petitioner proffered regarding his good behavior during the over seven months he spent in jail awaiting trial deprived petitioner of his right to place before the sentencer relevant evidence in mitigation of punishment. It can hardly be disputed that it did. The State does not contest that the witnesses petitioner attempted to place on the stand would have testified that petitioner had been a well-behaved and well-adjusted prisoner, nor does the State dispute that the jury could have drawn favorable inferences from this testimony regarding petitioner’s character and his probable future conduct if sentenced to life in prison. Although it is true that any such inferences would not relate specifically to petitioner’s culpability for the crime he committed, see Koon I, supra, at 536, 298 S. E. 2d, at 774, there is no question but that such inferences would be “mitigating” in the sense that they might serve “as a basis for a sentence less than death.” Lockett, swpra, at 604. Consideration of a defendant’s past conduct as indicative of his probable future behavior is an inevitable and not undesirable element of criminal sentencing: “any sentencing authority must predict a convicted person’s probable future conduct when it engages in the process of determining what punishment to impose.” Jurek v. Texas, 428 U. S. 262, 275 (1976) (opinion of Stewart, Powell, and Stevens, JJ.). The Court has therefore held that evidence that a defendant would in the future pose a danger to the community if he were not executed may be treated as establishing an “aggravating factor” for purposes of capital sentencing, Jurek v. Texas, supra; see also Barefoot v. Estelle, 463 U. S. 880 (1983). Likewise, evidence that the defendant would not pose a danger if spared (but incarcerated) must be considered potentially mitigating. Under Eddings, such evidence may not be excluded from the sentencer’s consideration.
  The State advances several arguments as to why the exclusion of petitioner’s proffered evidence was, nonetheless, not erroneous. First, the State contends that the trial court ruled only that petitioner’s witnesses could not offer incompetent lay opinion testimony regarding petitioner’s ability to adjust to prison life in the future. Eddings, the State argues, does not displace reasonable state-law rules regarding the competency of testimony. The record does not, however, support the State’s contention that the trial court’s ruling was no more than an evenhanded application of rules restricting the use of opinion testimony. It is true that petitioner’s request for a ruling on the admissibility of the testimony of the two jailers and the “regular visitor” was immediately preceded by an attempt to introduce his former wife’s opinion (ruled inadmissible by the trial judge, App. 10) regarding his prospects for adjustment to prison life. In seeking a ruling on the testimony of the three witnesses at issue here, however, petitioner made it clear that he expected them “to testify that [petitioner] has made a good adjustment” to jail. Id., at 11 (emphasis added). Defense counsel was not offering opinion testimony regarding future events. Under these circumstances, any ruling premised on the assumption that petitioner planned to present incompetent opinion testimony would have been — as the State conceded at oral argument — a “mistake.” Such a misunderstanding could by no means justify the exclusion of nonopinion evidence bearing on the defendant’s ability to adjust to prison life.
  Second, the State echoes the South Carolina Supreme Court in arguing that the trial court’s ruling was not improper because it did not prevent petitioner from introducing evidence of past good conduct in jail for purposes of establishing his good character, but only foreclosed the introduction of “irrelevant” evidence of his future adaptability to prison life. There is no clear support for this contention in the record of this case, as the trial court did not explicitly rely on any such distinction and appears to have excluded petitioner’s evidence of good conduct for any purpose whatsoever. The State’s proposed distinction between use of evidence of past good conduct to prove good character and use of the same evidence to establish future good conduct in prison seems to be drawn from the decision of the South Carolina Supreme Court in another case altogether, State v. Koon, 285 S. C. 1, 328 S. E. 2d 625 (Koon II), cert. denied, 471 U. S. 1036 (1985). There, the court stated that although “future adaptability to prison [is] irrelevant evidence because it does not bear on a defendant’s character, prior record, or the circumstances of his offense[,] . . . [p]ast behavior in prison does bear on a defendant’s character and, therefore, is relevant.” 285 S. C., at 3, 328 S. E. 2d, at 626. This distinction is elusive. As we have explained above, a defendant’s disposition to make a well-behaved and peaceful adjustment to life in prison is itself an aspect of his character that is by its nature relevant to the sentencing determination. Accordingly, the precise meaning and practical significance of the decision in Koon II and of the State’s argument is difficult to assess. Assuming, however, that the rule would in any case have the effect of precluding the defendant from introducing otherwise admissible evidence for the explicit purpose of convincing the jury that he should be spared the death penalty because he would pose no undue danger to his jailers or fellow prisoners and could lead a useful life behind bars if sentenced to fife imprisonment, the rule would not pass muster under Eddings. Since the trial court’s ruling in this case — whether or not it can credibly be said to be consistent with Koon II — sX least had this effect, it cannot stand under Eddings.
  Finally, the State seems to suggest that exclusion of the proffered testimony was proper because the testimony was merely cumulative of the testimony of petitioner and his former wife that petitioner’s behavior in jail awaiting trial was satisfactory, and of petitioner’s testimony that, if sentenced to prison rather than to death, he would attempt to use his time productively and would not cause trouble. We think, however, that characterizing the excluded evidence as cumulative and its exclusion as harmless is implausible on the facts before us. The evidence petitioner was allowed to present on the issue of his conduct in jail was the sort of evidence that a jury naturally would tend to discount as self-serving. The testimony of more disinterested witnesses — and, in particular, of jailers who would have had no particular reason to be favorably predisposed toward one of their charges— would quite naturally be given much greater weight by the jury. Nor can we confidently conclude that credible evidence that petitioner was a good prisoner would have had no effect upon the jury’s deliberations. The prosecutor himself, in closing argument, made much of the dangers petitioner would pose if sentenced to prison, and went so far as to assert that petitioner could be expected to rape other inmates. Under these circumstances, it appears reasonably likely that the exclusion of evidence bearing upon petitioner’s behavior in jail (and hence, upon his likely future behavior in prison) may have affected the jury’s decision to impose the death sentence. Thus, under any standard, the exclusion of the evidence was sufficiently prejudicial to constitute reversible error.
  The exclusion by the state trial court of relevant mitigating evidence impeded the sentencing jury’s ability to carry out its task of considering all relevant facets of the character and record of the individual offender. The resulting death sentence cannot stand, although the State is of course not precluded from again seeking to impose the death sentence, provided that it does so through a new sentencing hearing at which petitioner is permitted to present any and all relevant mitigating evidence that is available. Eddings, 455 U. S., at 117. The judgment of the Supreme Court of South Carolina is therefore reversed insofar as it affirms the death sentence, and the case is remanded for further proceedings not inconsistent with this opinion.
  It is so ordered.
  The relevance of evidence of probable future conduct in prison as a factor in aggravation or mitigation of an offense is underscored in this particular case by the prosecutor’s closing argument, which urged the jury to return a sentence of death in part because petitioner could not be trusted to behave if he were simply returned to prison. Where the prosecution specifically relies on a prediction of future dangerousness in asking for the death penalty, it is not only the rule of Lockett and Eddings that requires that the defendant be afforded an opportunity to introduce evidence on this point; it is also the elemental due process requirement that a defendant not be sentenced to death “on the basis of information which he had no opportunity to deny or explain.” Gardner v. Florida, 430 U. S. 349, 362 (1977).
  We do not hold that all facets of the defendant’s ability to adjust to prison life must be treated as relevant and potentially mitigating. For example, we have no quarrel with the statement of the Supreme Court of South Carolina that “how often [the defendant] will take a shower” is irrelevant to the sentencing determination. State v. Plath, 281 S. C. 1, 15, 313 S. E. 2d 619, 627, cert. denied, 467 U. S. 1265 (1984). In the case before us, there is no credible suggestion that petitioner sought to introduce evidence of his personal hygiene practices. Rather, petitioner apparently attempted to introduce evidence suggesting that he had been a well-behaved and disciplined prisoner. Such evidence of adjustability to life in prison unquestionably goes to a feature of the defendant’s character that is highly relevant to a jury’s sentencing determination.
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