This paper describes basic principles of systematics for psychiatric disorders such as the categorical and dimensional approach. It summarises validity aspects of the traditional psychiatric nosology and syndromatology. The importance and limitations of the dichotomy of schizophrenia and affective disorders, first suggested by Kraepelin, is reviewed in the light of results from modern research in the field of classification, follow-up and neurobiological studies, especially neurochemical, neurogenetic and neuroimaging studies. Current developments towards DSM-V and ICD-11 are critically reflected. The conclusion is reached that there might be insufficient data to establish a new systematics of psychoses. Therefore it might be premature to leave the Kraepelinian dichotomy totally although it has to be modified in the light of new research.