Suicide has been identified as a leading cause of premature death in autistic populations. Elevated autistic traits have also been associated with higher rates of self-harm, suicidal ideation, and suicidal self-harm in the general population, but this has yet to be examined in older age. Using baseline cross-sectional data from the PROTECT study, middle-age and older adults with high autistic traits (n = 276) had significantly higher rates of suicidal ideation, deliberate self-harm, and suicidal self-harm than an age/sex-matched comparison group (n = 10,495). These differences represented a 5- to 6-fold increase in likelihood for self-harming and suicidality. These findings, which remained when controlling for depression symptoms, suggest that middle-age and older adults with high autistic traits may be particularly at risk of self-harm and suicidal behaviours.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10803-022-05595-y.