An autopsy of an 11 years 5 months old boy with progeria is presented. Hyaluronuria, low growth rate of skin fibroblasts, decreased number of T-cells in lymphocyte subpopulation, increase of anti DNA antibody, and antibody for microsome of thyroid gland were detected clinically. He had suffered an attack of cerebral infarct and died of congestive cardiac failure. Pathologic findings were scleroderma-like skin atrophy, moderate arteriosclerosis of the aorta and great arteries, severely narrowed coronary sclerosis with an extensive subendocardial fibrosis, a large left cerebral infarct with pin-holed stenosis of both internal carotid arteries, cortical atrophy of thymus, and atrophic lymph nodes. The cardiac muscle fibers were slightly hypertrophied and measured 15.5 +/- 2.8 microns in diameter. Histologic findings suggest that increasing of collagen in the connective tissue may play an important role in progeria. Further study of metabolic disturbance in the connective tissue of progeria is necessary.