Very few studies have analyzed the role of social environments on substance abuse treatment outcomes among urban American Indians/Alaska Natives (AI/ANs). This study examined a measure of positive treatment response-abstinence from substance use at treatment discharge-among urban AI/ANs in Los Angeles County. The sample included all AI/ANs in outpatient drug-free (e.g., no methadone) treatment and residential treatment from 2004 to 2008 (N = 811). Predictors of abstinence at discharge were (a) having recovery-oriented social support and (b) not having a difficult living situation (i.e., experiencing family conflict and/or living with someone who uses alcohol and/or drugs). Higher levels of recovery-oriented social support in the past 30 days predicted abstinence during outpatient treatment. In residential treatment, retention of 90 days or more, high recovery-oriented social support, and not experiencing difficult living situations predicted abstinence. Suggestions for optimizing treatment outcomes among AI/ANs and areas of further research are provided.