Study Objectives:Sleep propensity and skin temperature are functionally related. In young adults, changes of skin temperature within the comfortable thermoneutral zone affect sleep-onset latency and vigilance performance. Aging is associated with both decreased thermosensitivity and poorer sleep. Our goal was to test whether subtle manipulations of core body and skin temperature affect sleep onset in elderly people without sleep complaints and in elderly insomniacs and whether the subjective perception of these mild body temperature manipulations is preserved with aging and insomnia.