OBJECTIVE: Psychiatric illness is a potent risk factor for suicide, rates of which differ markedly with age. The purpose of this study was to examine whether the psychiatric diagnoses of suicide victims vary predictably with age. METHOD: DSM-III-R axis I diagnoses of 141 persons aged 21 to 92 years who had completed suicide were established by the psychological autopsy method. Multiple logistic regression analyses were used to determine whether age, gender, or their interaction predicted the presence of specific disorders. RESULTS: One or more axis I conditions were diagnosable in 90.1% of the suicide victims. Substance use disorders were most frequent, followed by mood disorders and primary psychotic illness. Younger age at death was a significant predictor of substance abuse or dependence and primary psychoses, while older age predicted major mood disorders. Comorbidity of substance use and mood disorders was common. Among victims with substance abuse or dependence, older age at death predicted major depression; among victims with mood disorders, younger age at death predicted comorbid substance abuse or dependence. CONCLUSIONS: The distribution of psychiatric illnesses in suicide victims differs across the life course. Age-related patterns of addictive and psychotic disorders echo their prevalence in the general population. In contrast, the relationship between age and mood disorders among suicide victims is distinctly different from that of the general population. These findings suggest that risk for suicide increases with age in individuals with major affective illness. Depressed elderly men are particular targets for suicide prevention strategies.