There is an increasing criticism of the current operational diagnostic approach of ICD-10 and DSM-IV in psychiatry. It has not been possible to validate the respective diagnostic categories with neurobiological findings or to detect sharp boundaries between the diagnostic categories with respect to psychopathological symptoms. Therefore, dimensional diagnostic models are suggested in order to supplement the categorical diagnostic approach. Based on a historical review and a survey of the current criticism of the diagnostic approach of ICD-10 and DSM-IV proposals are made in order to solve the current problems. In conclusion, a multiaxial diagnostic model is suggested that comprises the axes "syndromes", "course types" and "etiology" and that may provide a bridge between the traditional categorical diagnostic approach and dimensional models.