The effect of age on sleep and the sleep EEG was investigated in middle-aged men (mean age: 62.0 years) and in young men (mean age: 22.4 years). Even though the older men reported a higher number of nocturnal awakenings, subjective sleep quality did not differ. Total sleep time, sleep efficiency, and slow wave sleep were lower in the middle-aged, while stage 1 and wakefulness after sleep onset were higher. The differences in wakefulness within nonREM-REM sleep cycles was most pronounced in the third and fourth cycle. In the older men, EEG power density in nonREM sleep was reduced in frequencies below 14.0 Hz, whereas in REM sleep age-related reductions were limited to he delta-theta (0.25-7.0 Hz) and low alpha (8.25-10.0 Hz) band. Slow-wave activity (SWA, power density in the 0.75-4.5 Hz range) decreased in the course of sleep in both age groups. The between-group difference in SWA diminished in the course of sleep, whereas the difference in activity in the frequency range of sleep spindles (12.25-14.0 Hz) increased. It is concluded that frequency and state specific changes occur as a function of age, and that sleep dependent decline in SWA and increase in sleep spindle activity are attenuated with age.