We compared clinical data, EEG, and video-EEG studies in a consecutive series of 20 patients with postictal psychosis (PP) to 150 consecutive epilepsy patients with complex partial (CPS) or generalized tonic-clonic (GTCS) seizures but without PP. There was a lucid interval between last seizure and onset of psychosis ranging from 2.3 to 72 h (mean, 25 h). Duration of PP ranged from 16 to 432 h (mean, 83 h). Age, sex, epilepsy type (partial vs. generalized), and history of febrile seizures were similar in the PP and control groups. Patients with PP had more frequent GTCS during monitoring than controls (2.8 vs. 1.3; P < 0.001). Patients with PP were more likely to have a history of encephalitis (P < 0.0001) and psychiatric hospitalization (P < 0.002). More patients with PP had bilateral interictal epileptiform discharges during monitoring than controls (P < 0.0002). Postictal psychosis most often develops in patients with bilateral dysfunction following a cluster of GTCS.