Quality of life (QOL) is a treatment outcome for substance use disorders that has largely been overlooked. Research suggests QOL is poor among persons with substance use disorders, even following treatment, but is unclear if this is primarily attributable to substance abuse itself or other life areas. Some evidence suggests other factors are responsible for low QOL, such as psychiatric distress. This paper examined QOL, its changes following treatment, and its contributors in two substance use disorder treatment studies (Homeless IV and EARTH) among persons who are homeless with co-occurring disorders. The purpose was to evaluate whether psychiatric distress should be an important target in treatment in order to improve QOL. To measure QOL, we converted scores from the SF-36 (Homeless IV) and the SF-12 (EARTH) instruments into SF-6D scores. Mixed models were used to analyze relationships among QOL, psychiatric distress, and drug abstinence. It was hypothesized that QOL would be lower than the general population in Homeless IV and even lower in EARTH because of the participants’ severe mental illness. We hypothesized QOL would improve following treatment. Finally, we hypothesized QOL would be most strongly associated with psychiatric distress rather than abstinence. Results supported QOL as worse in participants compared to the general population at baseline for Homeless IV (p<.001) and EARTH (p<.001) and at 6 months for EARTH (p<.001). Homeless IV participants showed overall improvement in QOL, with mean SF-6D scores increasing from 0.66 at iii baseline to 0.74 post-treatment and 0.71 at an 18-month follow-up (p<.001). EARTH participants did not show significant improvement in SF-6D scores from baseline (M=0.59) to post-treatment (M=0.60). Both abstinence and psychiatric distress were important contributors to QOL. Psychiatric distress showed the strongest association, with a 1% decrease in distress scores increasing SF-6D scores by 0.03% and 0.25% in Homeless IV and EARTH, respectively. This research concludes that QOL is poorer among persons with co-occurring disorders, and providers should target other life areas in addition to abstinence, as abstinence is not the only way to improve QOL. Inclusion of addiction treatment components to manage psychiatric distress can also be effective.