Contingency management (CM) treatments enhance drug abstinence. This study evaluated whether CM also improves quality of life and if these effects are mediated by abstinence. Across 3 independent trials, cocaine abusers in intensive outpatient treatment (n = 387) were randomly assigned to 12 weeks of standard treatment as usual or standard treatment with CM. The Quality Of Life Inventory (QOLI) was administered at baseline and at Months 1, 3, 6, and 9. Changes in QOLI scores over time differed significantly by treatment, with QOLI scores rising over time in CM participants and remaining stable in standard treatment participants. CM participants also achieved greater durations of abstinence, and duration of abstinence was correlated with posttreatment QOLI scores. During-treatment abstinence mediated the relationship between treatment condition and QOLI scores over time.