Postictal psychosis (PIP) is a common and clinically significant sequela of inpatient epilepsy monitoring. A series of 622 patients with complex partial epilepsy undergoing video-EEG evaluations as candidates for epilepsy surgery were evaluated, by structured psychiatric interview, for individual and family psychiatric histories, depression, anxiety, and features of personality disorders. No patient had psychotic symptoms at baseline. Twenty-nine developed a PIP episode during monitoring. The a priori hypotheses were that patients with PIP would have higher baseline schizotypal and paranoid personality ratings and a greater prevalence of histories of psychiatric treatment and family history of psychotic illness. However, only a higher prevalence of mood disorder among first- and second-degree relatives distinguished the patients who developed PIP on logistic regression analyses (odds ratio=3.49, P=0.001). Possible mechanisms linking vulnerability toward mood disorders and the development of psychotic symptoms in epilepsy are discussed.