• We compared the joint frequencies and reliabilities of the following sets of criteria for the diagnosis of schizophrenia: the New Haven Schizophrenia Index; the Carpenter, Strauss, Bartko (4-, 5-, 6-, and 7-item) system;DSM-III; Research Diagnostic Criteria (RDC; full and chronic); the Feighner system; and the 1975 criteria of Taylor and Abrams. The systems, of essentially equal reliability, varied sevenfold in their rates of diagnosing schizophrenia. Patients in whom schizophrenia was diagnosed by the lower-rate systems were likely to receive the same diagnosis by the higher-rate systems. This tends not to be the case when an affective syndrome is present.