Results revealed that three groups were at high risk of treatment failure: (1) unemployed generalized aggressors; (2) high school dropouts court mandated into substance abuse treatment; and (3) unemployed offenders court mandated into substance abuse treatment. Having a high school education, even among unemployed and impoverished offenders, increased the chances of treatment completion for both domestic batterer programs and substance abuse programs. Furthermore, the findings indicate the importance of separating generalized aggressors from family-only batterers in predicting treatment failure. The findings suggest that offenders who have basic life skill challenges, substance abuse problems, and general violent tendencies are less likely to benefit from domestic batterer treatment. It is suggested that courts and probation officers encourage offenders to complete high school or job training before mandating domestic violence treatment. Participants were 355 domestic batterers ordered to complete treatment by the Illinois Criminal Justice Information Authority (ICJIA) and the Administrative Office of the Illinois Courts (AOIC) during October and November 2000. Of the 355 batterers, 31.8 percent did not complete treatment. Variables under investigation included treatment failure and predictors of treatment failure. Data included the offender’s criminal histories, substance abuse problems, demographic characteristics, offense characteristics, prior mental health problems, and offense characteristics. Data were examined using two methods, which were then compared: (1) classification tree analysis (CTA); and (2) logistic regression models. The authors demonstrated that CTA, compared to logistic regression analysis, was a better statistical approach to determining groups of offenders at high risk for treatment failure. Future research should focus on the development of an assessment tool to determine risk of treatment failure. Tables, notes, references