Cycloid psychosis: an investigation of the diagnostic concept.

Seventy-three patients with the features of 'cycloid psychosis', adopted from Perris and Leonhard, were identified from case records. Information concerning background, presenting illness and follow-up was compared with that from the case-records of patients with schizophrenic, affective and schizoaffective psychoses. The characteristic features of 'cycloid psychosis' were a female predominance and a remittent course. The 'cycloid' group resembled the conventional groups in some respects, but differences from schizophrenic, affective and, to a lesser extent, schizoaffective groups were also striking. The factors which might account for the apparent independence of the 'cycloid' group from other diagnostic categories are discussed.