1. Test the effect of the brief intervention on drug use. We hypothesize that, among 12-18 year old medical patients who use drugs, the experimental intervention (two 60-minute motivational interviewing sessions) administered by a trained clinician will be at least 25% more effective than "standard care" (assessment/referral only) in decreasing drug use as measured by a 90-day Timeline Followback (6) (TLFB) calendar.