Day-reporting centers (DRCs) provide programming for probationers with a history of non-compliant behavior related to substance abuse, who are overrepresented among justice-involved men and women. While evaluations of DRCs demonstrate some effectiveness, results are mixed and less is known about predictors of program success. This evaluation compared indicators of program success between adult offenders with a substance use disorder (n = 144) and those with co-morbid mental illness (n = 113) at three DRCs. Analyses examined differences between and within groups on program completion, personal characteristics and subjective measures of well-being. Results indicated that program completers were more likely to be participants with substance use disorders only and to have a drug-related referring charge. No significant differences between groups on most measures of well-being were observed. Future investigations should consider tracking program dropouts to better understand program attrition and explore readiness to change in treatment programming.