The circadian distribution of motor activity and immobility of 14 unmedicated narcoleptics and matched controls was evaluated by monitoring continuous wrist motor activity 5 successive days and nights at home. Sleep was also assessed by sleep logs. The amplitude of the circadian rhythm of motor activity and immobility was significantly lower in narcoleptics than in controls. The variables that best distinguish narcoleptics from controls were the diurnal and nocturnal mean duration of uninterrupted immobility, which can be explained by excessive daytime sleepiness and frequent nocturnal awakenings, respectively. Thus, measures of diurnal and nocturnal motor activity and immobility appear useful for the objective assessment of some of the sleep-wakefulness manifestations of narcolepsy.