Adolescent decision making has been previously identified as risk factor for substance abuse as well as a proximal intervention target. The study sought to extend this research by evaluating the role of decision-making style in response to parent involvement in brief substance abuse interventions. Adolescents (aged 12 to 18 years; n = 259) identified in a school setting as abusing alcohol and marijuana were randomly assigned to complete 1 of 2 brief interventions (BIs), either a 2-session adolescent-only program (BI-A) or the 2-session adolescent program with an additional parent session (BI-AP). Interventions were manualized and delivered in a school setting by trained counselors. Adolescent decision-making style was evaluated at intake, and alcohol and marijuana use were evaluated at intake and at a 6-month follow-up assessment. Supporting past research with these interventions, BI-AP demonstrated overall stronger outcomes for marijuana when compared with BI-A. Across both intervention models, an adaptive decision-making style (i.e., constructive, rational) assessed at intake predicted greater reductions in marijuana use. A significant moderation effect emerged for alcohol outcomes. Adolescents with maladaptive decision-making tendencies (i.e., impulsive/careless, avoidant) demonstrated the largest benefit from the parental involvement in BI-AP, whereas those with a less impulsive style derived little additional benefit from parental involvement in regard to alcohol use outcomes. Implications for the tailoring of brief interventions for adolescent substance abuse are discussed.