Commitment to change is an innovative potential mediator and mechanism of behavior change (MOBC) that has not been examined in adolescents with substance use disorders (SUD). The Adolescent Substance Abuse Goal Commitment (ASAGC) questionnaire is a reliable and valid 2-scale measure developed to assess the adolescent’s commitment to either abstinence or harm reduction (HR) that includes consumption reduction as a stated treatment goal. The objective of this study was to examine the ASAGC’s ability to predict alcohol use treatment outcome. During sessions three and nine of a 10-week treatment program, therapists completed the ASAGC for 170 adolescents 13-18years of age with alcohol use disorder (AUD). Drinking behaviors were assessed during and after a continued-care phase until 12-month from study onset. Analysis of Variance results indicated that adolescents who reported no alcohol use had significantly higher scores on the commitment to abstinence scale than adolescents who reported alcohol use. None of the ANOVA models were significant for commitment to HR. When treatment outcome was examined, commitment to abstinence consistently predicted number of drinking days, number of heavy drinking days, and the maximum number of drinks post-treatment. In contrast, commitment to HR did not predict any of the drinking outcomes. These results suggest that the more adolescents were committed to abstinence during treatment, the less they used and abused alcohol after treatment completion. In addition to the ASAGC’s ability to differentiate between commitment to abstinence and commitment to HR, study findings demonstrate that goal commitment consistently predicts AUD treatment outcome.