The study also examined whether parental reports of other behaviors related to treatment outcome reliably reflected the self reports of adolescents. A further goal was to determine whether parental reports that were initially reliable continued to be reliable in reflecting the adolescents’ self-reports over time. Each of the 199 adolescents completed primary drug treatment at the same facility in the same 3-year period. The research followed the adolescents and their parents prospectively. The participants completed interviews with the same questionnaire at 3, 6, 9, and 12 months after completing primary treatment. The questionnaire contained questions designed to assess treatment success and relapse. The study used Cohen’s Kappa, differences between calculations of sample proportions, and paired-samples t tests to analyze the agreement between the parental and adolescent self-reports. Results revealed a high degree of agreement on questions regarding juvenile drug use for the first 3-month periods as measured by the Kappas and nonsignificant group mean differences, as well as similarly high concordance on outcome-related behaviors via nonsignificant paired-sample t tests. Findings indicated that parents can give reliable proxy information regarding their child’s post-treatment substance use and related behaviors if the parents are asked to report on observable behaviors and that parental reports are most reliable in the first 9 months following treatment. Tables, note, and 17 references (Author abstract modified)