Key PointsQuestionIs mortality among patients with nonfunctioning adrenal tumors (NFAA) higher than in the general population?FindingsIn this national retrospective register-based case-control study that included 17 726 cases and 124 366 controls, overall mortality among patients with NFAA was higher compared with controls (hazard ratio, 1.43; 95 CI, 1.38-1.48; adjusted hazard ratio, 1.21; 95% CI, 1.16-1.26) during the median follow-up period of 6.2 years (IQR, 3.3-9.6 years).MeaningThe results of this case-control study suggest that overall mortality among patients with NFAA was higher compared with controls.