The mental states of 23 epileptic psychotic patients and 10 patients with process schizophrenia were compared, using the Present State Examination. The epileptics displayed marked heterogeneity of psychiatric diagnoses. Disturbances of affect underlying the psychosis or presenting as manic-depressive psychosis were frequent and independent of the type of epilepsy. Schizophrenic psychosis, classified with psychopathological criteria similar to those used in the non-epileptic schizophrenic group, was significantly associated with temporal lobe epilepsy. Psychoses other than schizophrenia, however, were present in 5 out of 16 patients with temporal lobe epilepsy. These results support a relationship between schizophrenic symptoms and temporal lobe pathology and emphasize the need to use reproducible methods of diagnosis in psychiatric research.