In the year 2000 the German legislative decided to implement a case-dependent reimbursement system in an acute inpatient setting beginning in 2003. The German-Diagnoses Related Group System (G-DRGs) will adopt the refined version of the Australian-Diagnoses Related Group System (AR-DRG, version 4.1). Based on empirical data and expertś panels the acute psychiatric hospitals have been exempted from the adoption of the case-based payment system. With regard to national and international experiences in the development of patient classification systems in psychiatry and medical rehabilitation this article illustrates the development of a case group concept for patients with mental disorders.