Given the limited explanatory power of the available neurobiological findings, results of long-term follow-up studies should still be considered as one criterion among others in the development of psychiatric classification systems regarding schizophrenia and affective disorders. A total of 323 first hospitalized inpatients of the Psychiatric Department of the University Munich were recruited at index time and followed up after 15 years. The full follow-up evaluation including several standardized assessment procedures (AMDP, PANSS, SANS, DAS, GAS) could be performed in 197 patients. The patients originally diagnosed according to ICD-9 were re-diagnosed according to ICD-10 and DSM-IV, using SCID among others. Schizophrenic patients had a much poorer outcome than affective or schizoaffective patients in terms of negative syndrome, deficit syndrome, psychosocial impairments and GAS results, and a higher prevalence of a chronic course. The logistic regression analyses performed to find optimized predictor combinations for the prognosis of a chronic course found, for example, the total Strauss–Carpenter Scale score, male gender and several other psychopathological syndromes to be relevant predictors. The findings reflect some long-term related validity for the differentiation between schizophrenia and affective disorders. The Strauss–Carpenter Scale, male gender as well as several psychopathological syndromes are the most relevant predictors for chronicity.