Background: Changing addictive behavior is a complex process with high demands on motivation. The Transtheoretical Model of Behavior Change provides a theoretical framework for explaining and predicting behavioral change, although its predictive value for addiction is somewhat inconsistent. Objective: The aim of the present study is to extend the Transtheoretical Model of Behavior Change by investigating not only treatment motivation but also the predictive value of the type of drinking-related treatment goal. Additional predictors, such as substance-related and sociodemographic variables, are also included in analyses seeking to predict return to drinking during relapse prevention treatment for alcohol use disorder. Methods: In this observational study, 99 inpatients from a treatment center for alcohol use disorder were recruited. Treatment motivation was assessed in accordance with the Transtheoretical Model of Behavior Change, drinking-related treatment goal through a self-report questionnaire, and substance-related and sociodemographic variables via the clinic information system. Associations between the potential predictors and covariates were explored using stepwise logistic regression. Results: During treatment, 42.6% of participants had at least one relapse. Scoring higher on the action dimension at admission (OR = 0.81, p = .04) and being employed (OR = 0.37, p = .02) were significant predictors of abstinence during treatment. Conclusions: This study confirms that treatment motivation contributes to the prediction of treatment outcome, even when controlling for other variables. In future research, the underlying mechanisms of treatment motivation should be further explored.