Insulinoma with early-morning abnormal behavior.

We report a 65-year-old man with insulinoma who initially developed stereotypical behaviors and then progressed to more complex behaviors occurring early in the morning. He could not remember the events during the episodes. Insulinoma was diagnosed based on fasting blood glucose level of 15 mg/dl, high fasting immunoreactive insulin/blood glucose ratio (more than 0.3), and a tumor in the pancreas head by abdominal CT. Hypoglycemia caused by insulinoma should be considered as one of the mechanisms underlying abnormal nocturnal behaviors since the symptoms are very similar to those of sleep-related epilepsy, parasomnia, and night delirium.