Although sleep disturbance is a prominent feature of mania, its polysomnographic (PSG) features have received little study. To investigate more systematically the PSG characteristics of sleep in mania, all-night PSG evaluations were performed for two to four consecutive nights in 19 young manic patients (age range, 18 to 36 years), 19 age-matched patients with major depression, and 19 age-matched normal control subjects. Manic and depressed patients displayed nearly identical profiles of PSG abnormalities compared with normal control subjects, including disturbed sleep continuity, increased percentage of stage 1 sleep, shortened rapid eye movement latency, and increased rapid eye movement density. These results are similar to those reported in previous studies of major depression, and they are consistent with the possibility that the sleep disturbance in mania and major depression is caused by the same mechanism.