Objective: Currently, there is still a severe lack of methodologically sound empirical studies on acute psychiatric day hospital treatment in German-speaking countries that analyse the effectiveness of this increasingly important mode of service provision. Methods: Within a randomised controlled study design implemented at the Department of Psychiatry and Psychotherapy, Dresden University of Technology, 99 general psychiatric patients received conventional inpatient treatment and 92 patients received acute day hospital treatment. At up to four time-points during the index-treatment episode patients were assessed at different levels of outcome: Psychopathology was rated by researchers using the Brief Psychiatric Rating Scale (24-Item-Version), and patients evaluated their satisfaction with treatment (Patientenbogen zur Behandlungszufriedenheit); at admission and discharge patients also assessed their subjective quality of life (Manchester Assessment of Quality of Life). Mean scale scores of these instruments are used for the intention-to-treat- analysis. Discharge status on these scales as well as mean ratings on these scales within the index-treatment episode serve as measures of effectiveness. For statistically identifying differences between the two settings five linear (co-)variance-analytical models were calculated for each target variable. Four models were adjusted to baseline-rating or to the individual period spent in treatment. Results: Initially, both groups did not differ in their relevant socio-demographic and illness-related features. Day hospital treatment (87,7 days) lasted significantly longer than inpatient treatment (67,8 days). Only results from an unadjusted statistical model as well as from a model adjusted to the individual period of index-hospitalisation demonstrated superior effectiveness of day hospital treatment on the discharge status of psychopathological symptomatology. However, in all statistical models there were no systematic differences of treatment-effectiveness related to satisfaction with treatment and subjective quality of life. Conclusion: For the first time in German-speaking countries, this study provides evidence for the effectiveness of acute day hospital treatment as compared to conventional inpatient treatment. If detailed eligibility criteria for patients are used as defined here, approximately 30% of the general psychiatric patients in need of acute hospital-based treatment may be cared for in this special mode of day hospital service provision.