Abstract:The fact that the elderly are usually aware of early sleep onset and early morning awakening shows that the phase of sleep‐wake rhythms in the elderly is more advanced than that in young adults. Since it has been suggested that human sleep onset, morning awakening, sleep period and depth of sleep are highly influenced by body temperature rhythms, rectal temperature rhythms were analyzed in 7 healthy elderly and 7 healthy young adults under the condition with time cue. Although a significant 24‐hour period was found in the rhythms for all subjects, the phase of the rhythms in the elderly was more advanced than in the young adults. Moreover, a significant inverse correlation was observed between age and acrophase time in the elde