In this study we evaluated the internal consistency of the Brazilian Portuguese version of Teen Addiction Severity Index (T-ASI) and validated its "substance use" area. Evaluating 100 psychoactive substance abusers/dependent adolescents (SUD) and 108 adolescents without such diagnosis (NON-SUD), we found good correlations between the classification by the Composite International Diagnostic Interview (CIDI, used as "gold standard") and the severity (r = 0.73) and composite (r = 0.72) scores of the T-ASI. The area under the ROC curve was 0.88, showing a satisfactory correct classification rate. The internal consistency, evaluated by Cronbach's alpha coefficients, was considered good regarding the substance use (0.89), legal (0.81), and psychiatric (0.80) areas of the T-ASI. The Brazilian Portuguese version of T-ASI presented good internal consistency and a valid substance use area. A comparison between the groups regarding the answers to each question in all the areas was conducted in order to identify which questions in the T-ASI discriminate SUD from NON-SUD adolescents, to have a basis for the proposal of a shorter version of the instrument.