This article used the diagnostic criteria of the Diagnostic and Statistical Manual-Fourth Edition (DSM-IV) to compare the validity of a qualitative and a quantitative model of the abuse-dependence distinction for different psychoactive substances in samples of drug users drawn from drug treatment inpatients, general psychiatric patients, and the community. The hypothesis that DSM-IV abuse criteria differ from dependence criteria in kind rather than degree (a qualitative model) was only occasionally supported by confirmatory factor analyses of DSM-IV diagnostic criteria, by patterns of correlations of the two kinds of criteria with Addiction Severity Score (ASI) composites and measures of frequency of substance abuse, and by concurrent/prognostic validity analyses. However, the findings were consistent with a quantitative model of the abuse-dependence distinction that posits that abuse is a mild form of dependence. Whether abuse and dependence categories of users were established from separate DSM-IV criteria for abuse and dependence or from scores from a severity-of-dependence scale based on the pooled DSM-IV dependence and abuse criteria, abusers generally used drugs less than users in the dependence category and reported less problems associated with substance abuse on the ASI.