The authors studied sleep patterns of one hypomanic patient for seventeen of twenty-five consecutive nights. The patient was a forty-five-year-old salesman with a history of recurrent manic episodes. For several weeks prior to the sleep study, the patient had been developing a documented manic episode. He was not taking drugs and was not hospitalized. There was a marked reduction in actual sleep time and in slow-wave (stage 4) sleep, a slight reduction in stage 1 (REM) sleep, and an increase in time spent awake and drowsy. These findings were strikingly similar to the sleep patterns of patients suffering from psychotic depressive illness.