The association of and difference between urinalysis, self and parent collateral-report of alcohol and substance use at baseline, 3 and 9-month follow-up was assessed for 88 male and female adolescents from a treatment study. While urinalyses rates were higher than self and collateral-report, urinalyses and self-report did not differ significantly at follow-up. Associations between urinalyses and self-report were highest (r = 0.64, 0.69), followed by youth-/collateral report (0.49, 0.55), and urinalyses/ collateral-report (0.28, 0.43). Change in youth subjective substance use was associated with collateral subjective perceptions of use at follow-up. Higher false-negatives render collateral less reliable than self-report but necessary in the assessment process.