Substance use relapse rates are often high in the first months after discharge from inpatient substance abuse treatment, and patient adherence to aftercare plans is often low. Four residential addiction treatment centers participated in a feasibility study designed to estimate the efficacy of a post-discharge telephone intervention intended to encourage compliance with aftercare. A total of 282 participants (100 women, 182 men) with substance use disorders were included in this secondary analysis. The findings revealed that women were more likely than men to attend aftercare. This "gender effect" persisted after adjustment for a number of potential mediators.