Objective Premature discontinuation of treatment is one of the most frequent problems in inpatient detoxification treatment. The present study investigates the role of motivational factors. Methods In addition to the routinely collected diagnostic data, 85 patients were asked to complete questionnaires on the severity of symptoms of mental disorders, functional impairments and motivation for change at the time of admission and discharge. Results Patients who completed treatment indicated a significantly higher motivation for change than patients who terminated treatment prematurely. The contemplation phase had a predictive value (OR: 3.472) for treatment discontinuation. A successfully completed treatment significantly reduces the severity of symptoms of mental disorders and functional impairments. On the level of motivation for change, there is a significant increase. Conclusion In addition to the known risks of discontinuation, the measurable motivation for change at the beginning of treatment seems to be a possible marker for the course of treatment. Implications for clinical practice are derived.