Objective: Personality disorders (PDs) are common among patients with substance dependence, and antisocial PD in particular has been found to have a significant impact on treatment outcomes. Relatively little is known about other comorbid PDs, however. This study was designed to clarify the distribution of PDs among substance dependent patients and assess their role in treatment outcome.

Method: PDs and substance use disorders were diagnosed for 252 (181 male) consecutively admitted substance dependent inpatients using structured clinical interviews. A subsample of these (n = 104) were also followed for 1 year to monitor treatment outcome and relapse.

Results: Fifty percent of the patients were diagnosed with one or more personality disorders, but no consistent relationships between drug of choice and PDs were found. The likelihood of relapse, however, increased significantly with the diagnosis of a PD. Only 6% of the patients who received more than one PD diagnosis were maintaining sobriety at the end of 1 year compared with 44% of those with no PD diagnoses. A preference for cocaine was also a significant predictor of relapse.

Conclusions: The low participation rate for the treatment outcome study and other methodological limitations render the study results tentative. Nevertheless, the findings suggest that more attention should be given to Axis II disorders in substance dependence research and treatment.