The abnormal neuronal excitability underlying seizure disorders may alter behavior. Behavioral alterations associated with epilepsy can occur during the ictal period, especially in patients who suffer partial seizures of temporal or frontal lobe origin, or during the interictal period in the setting of chronic temporolimbic seizure discharges. We use case descriptions to illustrate behavioral presentations of epilepsy that resemble primary psychiatric illnesses, including schizophrenic psychoses, mood disorders, panic disorder, and dissociative disorders. The varied secondary psychiatric syndromes produced by epilepsy are elucidated by a consideration of normal functions of temporal and frontolimbic structures. The clinical pictures provide clues to the causes of primary psychiatric disorders.