The narcolepsy syndrome consists of excessive daytime somnolence, cataplexy, hallucinations, and sleep paralysis. Data on the effects of tranylcypromine are scant. We report on a patient with severe narcolepsy in whom administration of tranylcypromine led to freedom from hallucinations, nightmares, sleep paralysis, and rapid eye movements (REM), with considerable amelioration of cataplexy and increased daytime alertness. Muscle atonia and low-voltage desynchronized cortical activity during REM sleep did not change. Tranylcypromine warrants further study in narcolepsy.