Adolescents (aged 12-18 years) identified in a school setting as abusing marijuana and other drugs were randomly assigned to complete 1 of 2 brief interventions (BIs). Adolescents and their parent (N = 259) were randomly assigned to receive either a 2-session adolescent only (BI-A) or a 2-session adolescent and additional parent session (BI-AP). Interventions were manualized and delivered in a school setting by trained counselors. Adolescents were assessed at intake and at 6 months following the completion of the intervention. Using a latent construct representing 6-month marijuana use outcomes, current findings supported previous research that BI-AP resulted in superior outcomes when compared to BI-A. The presence of a marijuana dependence diagnosis at baseline predicted poorer outcomes when compared to youth without a diagnosis. Both baseline diagnostic status and co-occurring conduct problems interacted with intervention condition in predicting marijuana use outcomes. A marijuana dependence diagnosis resulted in poorer marijuana use outcomes within the BI-A condition when compared to BI-AP. Co-occurring conduct problems were associated with poorer marijuana use outcomes within the BI-AP intervention when compared to BI-A. Implications for implementing BIs given diagnostic status, parent involvement, and co-occurring conduct problems are discussed.