Elderly women had better recovery sleep than elderly men following 36-h sleep deprivation, as evidenced by higher sleep maintenance/efficiency and more slow wave sleep (particularly in the amount of stage 4 sleep). During recovery sleep, both groups showed REM latency reduction (two men and three women had seven sleep-onset REM periods out of a total of 40 recovery nights), decrease in percentage of early REM sleep and increase in whole-night REM sleep time. Total Mood Disturbance scores on the Profile of Mood States increased in both men and women following sleep deprivation (reflecting a decrease in vigor and increase in fatigue and tension). While the increase tended to be greater in women, in both groups self-ratings of mood returned to baseline after 1 night of recovery sleep. These observations underscore the importance of gender in determining late-life sleep structure and suggest that the ability of older women to achieve slow wave sleep and to have long uninterrupted sleep in greater than that of men.