Background: Skin thickness for parameter of skin aging has been analysed with various methods. Skin thickness variations between the young and the old has been studied with various methods such as biopsies, calipers, micrometers, computer tomography, ultrsonography. But none of these methods evaluates skin thickness exactly. Objective: For the evaluation of age-dependent skin thickness changes, we compared the skin thickness of an old-aged group and a young group with 20MHz-ultrasonography. Methods: In order to identify the skin thickness variation between different age groups, 60 subjects, 30 aged 23-33, and 30 over 60, were studied with 20MHz-high frequency ultrasonogrphy (Dermascan C, Cortex Technology, Hadsund, Denmark) on fourteen skin sites. This machine was designed to measure the thickness from the top of the epidermis to the bottom of the dermis. After storage of cross-sectional skin imaging, skin thickness was calculated with a computer assisted image-analysis program. Skin thickness of the old was analysed by age, sex, height and weight. (continue...) (Korean J Dermatol 1999;37(6): 719-725)