Previous reviews of outpatient interventions for adolescent substance abuse have been limited in the extent to which they considered the methodological quality of individual studies. The authors assessed 31 randomized trials of outpatient interventions for adolescent substance abuse on 14 attributes of trial quality. A quality of evidence score was calculated for each study and used to compare the evidence in support of different outpatient interventions. Across studies, frequently reported methodological attributes included presence of an active comparison condition, reporting of baseline data, use of treatment manuals, and verification of self-reported outcomes. Infrequently reported attributes included power and determination of sample size, techniques to randomize participants to condition, specification of hypotheses and primary outcomes, use of treatment adherence ratings, blind assessment, and inclusion of dropouts in the analysis. Treatment models with evidence of immediate superiority in 2 or more methodologically stronger studies included ecological family therapy, brief motivational interventions, and cognitive-behavioral therapy. (Contains 4 tables.)