We studied the effect of normal aging on human sleep. The subjects were 105 volunteers between the ages of 10 and 97 years. Polysomnography was done for three consecutive nights. Data collected on the second and third nights were scored according to the manual of Rechtschaffen and Kales. The sleep efficiency and the time percents of stage REM, stage 3, and stage 4 decreased gradually with age. The time percents of wakefulness stage 1, and stage 2 increased gradually with age. Stepwise regression analysis showed that sleep efficiency and the time percent of stage 3 + 4 were related to age. Sleep in the elderly is said to be characterized by more frequent awakenings, longer periods of light sleep (stage 1 + 2), shorter periods of deep sleep (stage 3 + 4) and REM sleep. The present results suggest that polysomnographic changes can be found even in young adults.