OBJECTIVES The objective of and concept behind the Marburg System of Quality Assurance and Therapy Evaluation (MARSYS) are presented. This a modular system with several instruments that is applicable for the evaluation of therapies with psychiatrically ill children and adolescents and can be employed in everyday routine care. METHODS The system was tested between 1999 and 2006 in the Marburg project on therapy evaluation in inpatient care. The article presents data from a complete user population with 1,321 patients. Data reporting on the practicability of the system comprise completeness of samples, dropout rates, acceptance of the evaluation among patients and parents, and the input of time and costs. RESULTS The results show that the system is very well suited to obtain significant findings with regard to the quality of outcome of the treatments. CONCLUSIONS The possibilities of implementing this system are discussed with regard to the matter of costs.