Affiliation with Alcoholics Anonymous (AA) and other 12-Step self-help groups is becoming more common at the same time as professional substance abuse treatment services are becoming less available and of shorter duration. As a result of these two trends, patients' outcomes may be increasingly influenced by the degree to which professional treatment programs help patients take maximum advantage of self-help groups. The present study of 3018 treated veterans examined how the theoretical orientation of a substance abuse treatment program affects (1) the proportion of its patients that participate in self-help groups, and, (2) the degree of benefit patients derive from participation in self-help groups. Patients treated in 12-Step and eclectic treatment programs had higher rates of subsequent participation in 12-Step self-help groups than did patients treated in cognitive behavioral programs. Furthermore, the theoretical orientation of treatment moderated the outcome of self-help group participation: As the degree of programs' emphasis on 12-Step approaches increased, the positive relationships of 12-Step group participation to better substance use and psychological outcomes became stronger. Hence, it appears that 12-Step oriented treatment programs enhance the effectiveness of 12-Step self-help groups. Findings are discussed in terms of implications for clinical practice and for future evaluations of the combined effects of treatment and self-help groups.