Roentgen evidence of 15 skeletal features was studied in 4 patients with progeria. Fourteen of the 15 features were noted in either 3 or all 4 patients. Four of these skeletal characteristics have not been noted previously—valgus deformity of the humeral head and neck, temporal variability in the appearance of epiphyseal ossification centers, laminations beneath the periosteum of bone, and transverse lines of increased density at the metaphyseal ends of the long bones. The 15 skeletal features could be accounted for on the basis of vascular and muscular alterations, and primary bone disturbances. Such diverse involvement of mesodermal derivatives suggests that the disorder in progeria originates during the early development of these structures. Pathological findings (sclerotic skin changes, subintimal fibrosis of vessels, multifocal interstitial myocardial fibrosis) and other evidence supports an abnormality of collagen metabolism which could be related to this mesodermal disorder.