To examine age at onset of substance abuse in relation to other factors of relevance to criminal behavior, we compared Life History of Aggression (LHA) scores, traits of psychopathy according to the Psychopathy Checklist--Revised (PCL-R), and violent recidivism in 100 violent offenders with early (before the age of 18) versus late onset of abuse or dependence. Of 56 subjects with a history of alcohol and/or drug abuse, an early onset was ascertained in 31. The duration of abuse did not correlate with the LHA and PCL-R scores or with violent recidivism, but the age at onset correlated strongly with all these factors and also remained their strongest correlate in multivariate models including childhood-onset attention deficit/hyperactivity disorder, conduct disorder, and drug abuse as covariates. Strong mathematical associations with aggression, psychopathy, and recidivism pointed to age at onset of substance abuse as a marker of possible complications that require preventive social, educational and medical measures.