OBJECTIVE The aims were to determine among patients with substance use disorder (SUD) whether those with antisocial personality disorder (ASPD) manifest less, the same, or more of the following: 1) temporal course of substance use, 2) severity of substance-related symptoms and problems, 3) familial SUD, 4) number and type of SUD diagnoses, and 5) extent of SUD treatment, as compared to patients without ASPD. DESIGN AND DEFINITION: Scheduled interviews using Diagnostic and Statistical Manual (DSM) criteria were used to determine ASPD, which required childhood conduct disorder plus adult antisocial behavior. Clinicians blind to the ASPD assessment collected the remainder of the data. METHODS Alcohol-drug treatment programs were located in two university medical centers. METHODS Six hundred and six voluntary patients aged 18 and older met diagnostic criteria for SUD. RESULTS SUD patients with ASPD reported more substance-related problems in seven out of eight areas of the interview-based Minnesota-Substance Abuse Problems scale. On a self-rated scale, the Michigan Assessment Screening Test/Alcohol-Drug, the difference was unremarkable. The ASPD group reported slightly, but significantly, more relatives with SUD. Lifetime use of tobacco and most illicit drugs was greater in the ASPD group. Age at first use of alcohol and tobacco was less in the ASPD group, but age at first use of other substances did not show a difference. Indicators of SUD course, such as years of use, days of use in the last year, duration of periods of abstinence, and number of self-help efforts showed no differences between the two groups. Types and numbers of SUD diagnoses showed no difference. However, all treatment indicators (i.e., lifetime number of admissions, modalities of care, days of care, and cost of care) were significantly higher in the ASPD group. A regression analysis revealed that family and legal problems remained strongly associated with ASPD, but other substance-related problems and SUD treatment dropped out. CONCLUSIONS Despite the many similarities in SUD among those with and without ASPD, the morbidity in the ASPD as measured by number and types of substance-related problems and by all treatment variables is considerably greater. Legal and family problems appear to be powerfully associated with ASPD and predictive of other problems as well as SUD treatment.