In elderly humans, daytime naps are common, nocturnal sleep is poorly consolidated, and the sleep period often begins and ends earlier than in young adults. Because previous work has suggested that rodents may provide a useful animal model for these changes, we conducted a detailed investigation of sleep patterns in 11 young adult and 9 old mice. Mice were surgically implanted for chronic EEG recording, and sleep state was monitored over multiple circadian cycles. During the active phase, old mice spent more time asleep and had shorter wake episodes compared with young mice. During the rest phase, old mice spent more time awake than young mice, and tended to have shorter episodes of sleep. No evidence was found, however, for earlier timing of sleep in older mice. These results suggest that the mouse may provide a suitable animal model for further study of certain age-related changes in temporal distribution of sleep and wakefulness.