The 24-hour temporal regulation of hormonal secretions results from the interaction of an endogenous circadian pacemaker and of sleep-wake homeostasis, a mechanism linking the timing and the intensity of sleep to the duration of prior wakefulness. A prominent age-related alteration of hormonal circadian rhythmicity is characterized by a reduction in rhythm amplitude and a phase advance. At the same time, the sleep-wake pattern undergoes major modifications, with a spectacular decrease in “restorative” sleep stage from early adulthood to mid-life, followed thereafter by sleep fragmentation and a decrease in total sleep time. Age-related sleep and endocrine-metabolic alterations frequently interact with each other.