Objective: Strong opinions have been voiced about the "fit" between 12-step treatment, community-based 12-step practices, and American Indian beliefs and values. Little is known, however, about the relative benefit of 12-step programs for urban American Indians, although they are the most widely accessed type of treatment by American Indians. This study investigated rates of 12-step attendance, attrition, and substance use outcomes for American Indians for 9 months relative to non-Hispanic White participants. Method: This study compared urban American Indian (n = 63) and non-Hispanic White (n = 133) 12-step attendance, attrition, and substance use over 9 months. The sample was formed by merging data from two prospective single-group longitudinal studies investigating behavior change in community-based 12-step programs. Participants were interviewed at baseline and at 3-, 6-, and 9-month follow-ups. No intervention was provided. Participants were recruited from Alcoholics Anonymous meetings in the community and as they presented for outpatient substance use disorder treatment. Substance use and patterns of 12-step attendance were measured using the Form 90 calendar-based interview, and the General Alcoholics Anonymous Tools of Recovery was administered to assess the adoption of prescribed 12-step practices and beliefs. Results: Trajectories in 12- step meeting attendance over 9 months did not differ between American Indian and non-Hispanic White participants. However, American Indian participants discontinued 12-step attendance significantly less often than non-Hispanic White participants. Higher rates of 12-step attendance predicted increased alcohol abstinence and decreased drinking intensity for both American Indian and non-Hispanic White participants. Twelve-step attendance was unrelated to later illicit drug use for both American Indian and non-Hispanic White participants. Conclusions: Community-based 12-step program attendance is associated with drinking reductions among urban American Indians.