200 first admissions with functional psychoses were interviewed with PSE and rated simultaneously according to different diagnostic criteria (ICD-9, RDC, DSM-III, St. Louis, Taylor, Vienna Research Criteria). At follow-up 7 years later 186 patients could be traced and a course diagnosis was applied to each patient. Temporal stability of diagnostic criteria was calculated for ICD-9, RDC and DSM-III by stability coefficient and kappa values and was used as a criterion for validity. Schizophrenia and affective disorder display considerable stability over time, no matter whether one uses ICD-9, RDC or DSM-III. The data for schizoaffective disorder are less impressive, the stability coefficient is much higher for schizoaffective bipolar than for schizoaffective depressive patients.