BACKGROUND: It remains unclear whether specific clinical factors contribute to heterogeneity in the timing of the onset of nonfatal suicidal behavior. This knowledge could have important implications for suicide prevention. METHODS: Using a nationally representative US adult sample, the second wave of the National Epidemiologic Survey on Alcohol and Related Conditions (2004-2005; n = 34,629), we compared the characteristics of 4 different suicide attempter groups: those who first attempted (1) before 18 years, (2) from 18 to 34 years, (3) from 35 to 49 years, and (4) at 50 years or older. Specifically, DSM-IV psychiatric disorders that occurred before the first suicide attempt, childhood maltreatment experiences, parental history of psychiatric disorders, and sociodemographic characteristics were examined. RESULTS: Most first nonfatal suicide attempts (85.3%) occurred before age 35 years. Compared with suicide attempts occurring from 18 to 34 years, suicide attempts occurring before 18 years were more strongly associated with childhood maltreatment and less strongly linked to lifetime prior psychiatric disorders, whereas first suicide attempts occurring at 35 years and older were more strongly associated with a prior lifetime history of substance use disorders, including alcohol use disorder and nicotine dependence, and mood disorders, including mania/hypomania and dysthymic disorder between 35 and 49 years and major depressive episode at 50 years and older (all P < .05). CONCLUSIONS: These results suggest age differences in risk factors for first nonfatal suicide attempt. Improving early detection and treatment of psychiatric disorders and preventing childhood maltreatment may have broad benefits to reduce the burden of suicidal behavior at all ages.