To explore the concordance between urine drug screen (UDS) results and self-report of cocaine use, results in a pharmacologic treatment trial for cocaine dependence were evaluated. Subjects with at least two occurrences of a positive UDS for cocaine were characterized as either an under-reporter (UR, n = 43) or a truthful reporter (TR, n = 32). Interestingly, URs attended more study sessions and were more likely to complete the study. Significant differences were found in cocaine use patterns and the prevalence of Axis I and Axis II disorders. This information may be important in guiding the judicious use of UDS in clinical and research settings.