First-degree relatives of narcoleptic subjects (probands) may have sleep pathology related to the transmission of the disorder through their family members. The authors examined four groups: probands (n = 96), first-degree relative (n = 337), environmental reference (n = 85), and general population (n = 6,694) groups. Compared with the general population, family members have a 75-fold increased risk for narcolepsy. They are also at greater risk for insufficient sleep syndrome (odds ratio [OR] 6.1), nocturnal eating (OR 5.7), and adjustment sleep disorder (OR 3.1).