A review of a number of major studies of the outcome of schizoaffective disorders, focusing on how schizoaffective disorders should be viewed diagnostically, is presented. An analysis is made of various research methods used, including prospective, retrospective, and prognostic approaches. Results of the analysis suggest that prospective studies are more valuable. The research results on outcome question the thesis that schizoaffective disorders are only affective disorders. Overall, the mixed results reveal that the outcome of schizoaffective disorders is poorer than that of affective disorders and better than that of schizophrenia. Since outcome is one type of validating criterion which can be used for establishing diagnostic categories, the results question aspects of the DSM-III system of categorizing schizoaffective disorders. We suggest that mood-incongruent psychotic symptoms either influence outcome negatively or are associated with other features which influence outcome negatively.