Narcolepsy is the most prevalent of the primary disorders of vigilance. It is relatively easy to identify in presence of clearcut cataplexy and other REM-sleep related symptoms, i.e. sleep paralysis and hypnagogic hallucinations. Otherwise, one must rely on demonstration of sleep onsets in REM during night and daytime polygraphy, and on the very strong association with the HLA gene DQB1*0602. METHODS With the advent of modafinil, treatment of narcolepsy has been substantially modified. New strategies are an improvement over amphetamines both in terms of side effects and long-term outcome. Most cataplectic attacks can be controlled by tricyclics or other antidepressants. METHODS Major advances in pathophysiology and etiology have been obtained through an animal model of the disease, canine narcolepsy. Pharmacological studies point to the importance of alpha-1 adrenergic mechanisms in cataplexy, while dopaminergic systems seem more involved in generating sleepiness. As concerns genetics of this autosomal recessive disease, there is an equivalent of the human HLA association in the form of an immunoglobulin gene (mu-switch) linkage. Narcolepsy research is now looking for other genes, for which familial cases may give clues.