Patients dually-diagnosed with mental illness and chemical abuse often comply poorly with treatment. The present study tested the hypothesis that attendance at a day treatment program could be increased by offering modest incentives for regular participation. Fifty-three patients, enrolled in a voluntary day treatment program for the mentally ill chemical abuser, were studied for twelve weeks. Attendance was monitored for (a) 4 weeks prior to the incentive intervention; (b) 4 weeks during which an incentive was provided for regular attendance; and (c) 4 weeks following the incentive. The incentive consisted of modest rewards (e.g., coupons from a local restaurant) offered at the end of the week to all patients who attended the program for at least 5 hours a day on at least 3 days in a given week. The results demonstrated that modest incentives can enhance the attendance patterns of the dually-diagnosed.