Although adherence to aftercare therapy in substance abuse treatment is associated with improved outcome, little research has explored the effects of adherence interventions on outcome. We compared 20 graduates of our 28-day intensive treatment program who received a standard aftercare orientation with 20 graduates who received this intervention plus social reinforcement of aftercare group therapy attendance. The social reinforcement group showed less alcohol use than the standard care group at a 6-month follow-up assessment as measured by the Addiction Severity Index (ASI), but not less drug use. Additionally, compared to standard care, the social reinforcement participants were more likely to be abstinent at the 6-month follow up (76% vs. 40%). The groups did not differ on hospital readmission rates over a 12-month follow-up period. Additionally, the social reinforcement group showed better long-term aftercare attendance compared to the standard care group.