Objective:  Schizoaffective disorders are well established. Nevertheless, the definition in the International Classification of Diseases (ICD)‐10 and the Diagnostic and Statistical Manual (DSM)‐IV are insufficient. Method:  Critical review of the literature from Kahlbaum (1863) to the 21st century. Results:  Many authors have described people suddenly developing a disorder with both ‘schizophrenic’ and ‘affective’ symptoms. In DSM‐IV and ICD‐10, the schizoaffective disorder is defined as the concurrent occurrence of schizophrenic symptoms with a major affective disorder. However, there is no reason for a chronological distinction regarding the co‐existence of schizophrenic and affective symptomatology. Moreover, longitudinal aspects are not included in the definitions. Conclusion:  Two types of schizoaffective disorder must be distinguished: the ‘concurrent’ and the ‘sequential’ type. The first includes people having only a coincidence of schizophrenic and affective symptoms. The ‘sequential’ type is defined as the schizoaffective disorder under a longitudinal aspect subsuming disorders with a symptom change between different episodes. Consequences for further research are discussed in detail.