Narcolepsy afflicts more than 200,000 Americans. In most cases the first symptom of the disease, excessive daytime sleepiness, develops during childhood or adolescence. This initial presentation is followed by cataplexy or other auxiliary symptoms several years later. Not infrequently, many years pass before the proper diagnosis of narcolepsy is made. Narcolepsy is a chronic lifelong disease without periods of remission. Excessive daytime sleepiness, inappropriate sleep attacks, and the pathognomonic symptom of cataplexy, are diagnostic of narcolepsy. Confirmation of the disease is made by a multiple sleep latency test. Although still not being used for diagnostic purposes, the association between narcolepsy and the human leukocyte group A (HLA) antigen DR2 is the strongest so far described for any disease. With the help of psychosocial support, therapeutic naps, and medications, the patient with narcolepsy may be able to lead a normal life. Methylphenidate and imipramine are the two most widely used drugs for the treatment of daytime somnolence and cataplexy, respectively.