The goal of this trial is to evaluate the efficacy of an enhanced Teen Marijuana Check-Up protocol to reach and intervene with non-treatment seeking adolescents who use marijuana heavily. Two hundred fifty adolescents who use marijuana heavily will receive a 2-session individual motivational enhancement therapy. All participants will also be offered the opportunity, over a 12-month period, to repeatedly re-initiate marijuana counseling. Participants will be randomly assigned to receive one of two types of periodic follow-up contacts: Motivational interviewing-based Marijuana Check-Ins (MCI) or Computer Based Control (Comp) sessions.