Sixteen patients with progressive diaphyseal dysplasia (PDD) and aged six months to 76 years were examined. Fourteen cases were hereditary, two were not. The progression of the radiologic manifestations in 13 patients who were followed up from 1 to 32 years and the computed tomography (CT) scans from five patients were obtained. The progression of PDD was slow and unpredictable, from minimal endosteal thickening of the mid-diaphyses in one pair of long bones to severe sclerosis of long bones, skull, and vertebrae. The severity of the osseous changes was not age dependent. A six-stage system was used to grade the severity of involvement and progression of PDD. CT scans demonstrated muscle mass that was preserved and showed the distribution of the osteosclerotic process, which was irregular and inhomogeneous. CT scanning was advantageous over plain radiography in this respect. Endosteal involvement was more extensive than periosteal thickening. CT scans also showed a distinct pattern of vertebral sclerosis that was confined to the posterior areas of the vertebral body and arches. In light of the paucity of characteristic clinical signs of PDD, the recognition of the radiologic features is mandatory for the diagnosis of this disease.