Objectives. We examined differences in substance abuse treatment outcomes between American Indians and their non–American Indian counterparts in California, during 2000 to 2002. Methods. A total of 368 American Indians and a matched sample of 368 non–American Indians from 39 substance abuse treatment programs in 13 California counties were assessed at multiple time points. Records on arrests, driving while under the influence of alcohol or drugs, and mental health care were obtained 1 year before and 1 year after treatment entry. Differences in pretreatment characteristics, services received, treatment satisfaction, treatment completion and retention, and outcomes were examined. Results. Pretreatment problems were similarly severe among American Indians and non–American Indians. About half in both groups either completed treatment or stayed in treatment more than 90 days; American Indians in residential care had significantly shorter treatment retention. American Indians received fewer individual sessions and out-of-program services, especially for alcohol abuse, but were nevertheless generally satisfied with their treatment. Both groups improved after treatment, with American Indians demonstrating greater reductions in arrests than non–American Indians. Conclusion. American Indians benefit from substance abuse treatment programs, although the type and intensity of services offered could be improved.