It is estimated that from 20 to 60% of substance abusers meet criteria for Antisocial Personality Disorder (APD). An accurate and reliable diagnosis is important because persons meeting criteria for APD, by the nature of their disorder, are less likely to change behaviors and more likely to relapse to both substance abuse and high risk behaviors. To understand more about the reliability of the disorder and symptoms of APD, the Diagnostic Interview Schedule Version III-R (DIS) was administered to 453 substance abusers ascertained from treatment programs and from the general population (St Louis Epidemiological Catchment Area (ECA) follow-up study). Estimates of the 1 week, test-retest reliability for the childhood conduct disorder criterion, the adult antisocial behavior criterion, and APD diagnosis fell in the good agreement range, as measured by kappa. The internal consistency of these DIS symptoms was adequate to acceptable. Individual DIS criteria designed to measure childhood conduct disorder ranged from fair to good for most items; reliability was slightly higher for the adult antisocial behavior symptom items. Finally, self-reported 'liars' were no more unreliable in their reports of their behaviors than 'non-liars'.