Objective measures of drug use are very important in treatment outcome studies of persons with substance use disorders, but obtaining and interpreting them can be challenging and not always practical. Thus, it is important to determine if, and when, drug-use self-reports are valid. To this end we explored the relationships between urine drug screen results and self-reported substance use among adolescents and young adults with opioid dependence participating in a clinical trial of buprenorphine-naloxone. In this study, 152 individuals seeking treatment for opioid dependence were randomized to a 2-week detoxification with buprenorphine-naloxone (DETOX) or 12weeks of buprenorphine-naloxone (BUP), each with weekly individual and group drug counseling. Urine drug screens and self-reported frequency of drug use were obtained weekly, and patients were paid $5 for completing weekly assessments. At weeks 4, 8, and 12, more extensive assessments were done, and participants were reimbursed $75. Self-report data were dichotomized (positive vs. negative), and for each major drug class we computed the kappa statistic and the sensitivity, specificity, positive predictive value, and negative predictive value of self-report using urine drug screens as the "gold standard". Generalized linear mixed models were used to explore the effect of treatment group assignment, compensation amounts, and participant characteristics on self-report. In general, findings supported the validity of self-reported drug use. However, those in the BUP group were more likely to under-report cocaine and opioid use. Therefore, if used alone, self-report would have magnified the treatment effect of the BUP condition.