The age-dependent decrease of skin thickness was studied with a morphometric procedure on upper inner arm skin biopsies. Epidermal thickness decreased somewhat faster in men (7.2% of the original value/decade) than in women (5.7%). The total dermal thickness decreased at about the same rate in men and women (6%/decade). The thickness of the superficial layer of the dermis exhibited a biphasic evolution with age and these variations were not significantly different between men and women because of the large individual variations. This may be due partially to the difficulties of delineating with precision the limit between superficial and reticular dermis. These results are somewhat lower than those obtained by physical measurements of skin thickness. This may be due to fixation artifacts and also to the overestimation of skin thickness by physical measurements.