Body temperature, vigilance, memory, information processing and motor function were examined in 10 unmedicated narcoleptics and 10 matched controls at four different times of day. Time of day and body temperature were not related to performance. Narcoleptics displayed selective cognitive deficits in response latency, word recall, and estimation of frequency. Narcoleptics did not differ from controls in motor speed, vigilance, information processing speed or decision-making accuracy. We propose that a perceptual-encoding deficit may underlie the problems in memory and complex reaction time associated with narcolepsy.