The classification of functional psychoses and its implications for prognosis.

One hundred and eighty-three patients suffering from functional psychoses were diagnosed according to ICD-8, RDC, and DSM-III criteria, and the concordance rates for the diagnoses compared. The heterogeneity of the diagnosis 'schizoaffective psychosis' as defined by these systems became clear. With respect to prognosis, the DSM-III diagnosis of schizophrenia was most closely related to poor outcome. Affective psychoses and schizoaffective psychoses, as well as DSM-III 'schizophreniform disorders', demonstrated a favourable prognosis.