A common recommendation for youth treated for substance abuse is to attend 12-step groups. However, little is known regarding the effects of this adult-derived prescription on substance use outcomes for teens. This study examined (a) the relation between 12-step attendance and substance use outcome in the 6 months postdischarge from inpatient care and (b) a process model of how 12-step attendance during the first 3 months postdischarge affects proximal outcomes of motivation, coping, and self-efficacy, measured at 3 months, and how these, in turn, affect ultimate substance use outcome in the following 3 months. Adolescent inpatients (N = 99) were assessed during treatment and 3 and 6 months postdischarge. Results revealed modest beneficial effects of 12-step attendance, which were mediated by motivation but not by coping or self-efficacy. Findings suggest that closer attention be paid to motivational factors in the treatment of adolescent substance abuse.