Little is known about sleep and the effects of total sleep loss in the 'old old' (i.e., 80-year-olds). We investigated sleep, mood, and performance responses to acute sleep deprivation in healthy 80-year-olds (n = 10) and 20-year-olds (n = 14). The protocol consisted of three nights of baseline sleep, one night of total sleep deprivation, and two nights of recovery sleep. Mood and vigilance were tested using visual analog scales and a Mackworth clock procedure in the morning and evening of each study day. Daytime sleepiness was measured by five naps on the days following the third and sixth nights. Old subjects had lower sleep efficiency and less delta sleep than young subjects. However, sleep continuity and delta sleep were enhanced in both groups on the first recovery night, indicating that sleep changes in old subjects are at least partially reversible by this procedure. Surprisingly, young subjects had shorter daytime sleep latencies than the old, suggesting a greater unmet sleep need in the former group. Mood and performance were disturbed by sleep loss in both groups, but to a greater extent among the young. This suggests that acute total sleep loss is a more disruptive procedure for the young than for the old.