OBJECTIVE: This study sought to elucidate the relation of clinical, neuropsychological, and seizure variables to chronic and postictal psychoses in patients with temporal lobe epilepsy. METHOD: Forty-four patients with treatment-refractory temporal lobe epilepsy were given formal psychiatric evaluations; 29 patients had no psychiatric disorder or a nonpsychotic disorder, eight patients had postictal psychoses, and seven patients had chronic psychoses. Comparisons of clinical, neuropsychological, magnetic resonance imaging, and seizure variables were made between the nonpsychotic and the psychotic patients and, secondarily, between the patients with transient postictal psychoses and those with chronic psychoses. RESULTS: Bitemporal seizure foci, clustering of seizures, and absence of febrile convulsions were associated with both postictal psychoses and chronic psychoses. Younger age at onset of epilepsy and lower verbal and full-scale IQs differentiated the patients with chronic psychoses from those with postictal psychoses. CONCLUSIONS: Patients with temporal lobe epilepsy with chronic and postictal psychoses show similar profiles of clinical and seizure variables, suggesting shared etiologic factors. These factors may increase the propensity to develop psychotic symptoms, while other factors, such as time of onset of epilepsy and underlying neuropathology, may determine whether transient or chronic psychotic symptoms develop. Even among patients with treatment-refractory temporal lobe epilepsy, a specific subgroup of patients, characterized by bitemporal seizure foci, an absence of febrile convulsions, and a history of clustering of seizures, appears to be particularly prone to develop psychotic disorders. A process similar to secondary epileptogenesis may be involved in the development of the psychoses.