A standard program of computed tomographic (CT) scanning of the human skeletal muscular system was developed. Scans were obtained on five levels: the neck, the shoulder girdle, the pelvic girdle, the thigh, and the lower leg. The normal size and density of several muscles were determined. CT scans were also obtained in patients with various neuromuscular diseases. Several types of lesions were found, and their morphologic descriptions and quantitative data are presented. It is concluded that CT opens new possibilities for the evaluation of muscular atrophy and hypertrophy.