This study examined the proximal effects of alcohol and drug use on adolescent illegal activity. Four years of longitudinal data from the Pittsburgh Youth Study were analyzed for 506 local male adolescents. Participants reported committing offenses against persons more often than general theft under the influence of alcohol or drugs. Aggressive acts were more often related to self-reported acute alcohol use than to marijuana use. Those who reported committing illegal acts under the influence reported committing offenses with other people and being arrested more often than those who did not. Offenses under the influence were more prevalent among heavier alcohol and drug users, more serious offenders, more impulsive youth, and youth with more deviant peers. There were no significant interaction effects of alcohol and drug use with impulsivity or deviant peers in predicting whether illegal acts were committed under the influence. The association between drug use and illegal activity during adolescence is complex.