Rates of suicide differ markedly as a function of age and gender. In a great majority of countries that report suicide statistics, rates are higher in the elderly than in younger age groups. Few data are available to determine whether this age-related pattern of rates is reflected in a differential prevalence of other factors known to be associated with increased suicide risk. Using the psychological autopsy method, researchers have established the distribution of psychiatric diagnoses in samples of adolescents, young adults, and elders who have committed suicide, and in victims across the life course in community-based populations. Review of those studies reveals that affective disorders, substance use disorders, and their comorbidity are common in completed suicides of all ages. Although methodologic issues and cohort and period effects limit the conclusions that can be drawn, comparison by age within and between studies further suggests that depressive illness is more common and substance abuse less prevalent in later-life victims. That the aging process itself (biological, psychological, and social) may account for the observed pattern has important implications for further research and the design of intervention strategies. There is a need for more coordinated and comprehensive study of psychopathological correlates of suicide across the life course in a broad range of cultures.