To evaluate the effect of intermittent hypoxemia on neuropsychological functioning, neuropsychological tests were administered to 14 sleep apnea patients, a control group of 10 patients with other disorders of excessive somnolence, and another control group of 14 healthy volunteers. The sleep disorder groups were matched on two measures of sleepiness. It was found that sleep apnea patients performed significantly worse than both controls on 7 of 14 neuropsychological measures and on a rating of global neuropsychological impairment. The overall level of performance reflected only moderate impairment. Within the sleep apnea group, hypoxemia severity was significantly correlated with deficits on measures of motor and perceptual-organizational ability.