Chronic idiopathic hyperphtsphitasia is a rare disease of childhtod characterized by generalized cortical thickening of the long bones and skull, resulting in marked bone deformities, and by a sustained elevated serum alkaline phosphatase value. The roentgenographc and pathological findings in this disease were indistinguishable from adult Paget's disease of bone. The associated pseudoxanthoma elasticum in the presented case may reflect a common underlying defect in these two diseases.