This study evaluates the effectiveness of motivational enhancement therapy/cognitive behavioral therapy-5 (MET/CBT-5) when delivered in community practice settings relative to standard community-based adolescent treatment. A quasi-experimental strategy was used to adjust for pretreatment differences between the MET/CBT-5 sample (n = 2,293) and those who received standard care (n = 458). Results suggest that youth who received MET/CBT-5 fared better than comparable youth in the control group on five of six 12-month outcomes. A low follow-up rate (54%) in the MET/CBT-5 sample raised concerns about nonresponse bias in the treatment effect estimates. Sensitivity analyses suggest that although modest differences in outcomes between the MET/CBT-5 nonrespondents and respondents would yield no significant differences between the two groups on two of the six outcomes, very large differences in outcomes between responders and nonresponders would be required for youth receiving MET/CBT-5 to have fared better had they received standard outpatient care.