This study, based on a nationally representative, epidemiologic sample (N = 43,093, response rate 81%), compared sociodemographic and family history correlates, antisocial personality disorder (ASPD) symptom patterns, and Axis I and Axis II comorbidity, among adults with DSM-IV ASPD who reported onset of conduct disorder (CD) in childhood (<age 10) versus adolescence (> or =age 10). Prevalence of each ASPD diagnostic criterion and comorbid lifetime disorder was estimated. Logistic regression was used to examine associations of childhood-onset CD with ASPD symptom patterns and comorbid disorders. Among the 1422 respondents with ASPD, 447 reported childhood-onset CD. Childhood-onset respondents were more likely than adolescence-onset respondents to endorse CD criteria involving aggression against persons, animals, and property before age 15, and to endorse more childhood criteria and lifetime violent behaviors. Childhood-onset respondents displayed significantly elevated odds of lifetime social phobia, generalized anxiety disorder, drug dependence, and paranoid, schizoid, and avoidant personality disorders, but significantly decreased odds for lifetime tobacco dependence. Childhood-onset CD appears to identify a more polysymptomatic and violent form of ASPD, associated with greater lifetime comorbidity for selected Axis I and Axis II disorders, in nonclinical populations.