The results of the treatment of 12 patients with hypophosphataemic vitamin D-resistant rickets, 4 similar patients who were first diagnosed in adulthood, and 2 adult patients with hypophosphataemic vitamin D-resistant osteomalacia are presented. Treatment with a high dosage of Vitamin D2 was begun between 1 1/2 and 7 years of age. The dose of Vitamin D2 required for the treatment of rickets varied widely depending on the severity of the process and the age of the patient. Four patients with leg deformities required osteotomy or other operations. In other patients deformities improved with medical treatment alone. Dwarfism and severe deformity of the legs were characteristic features in rickets first diagnosed in adulthood. Radiographic features were Looser's zones, a coarse trabecular pattern, increased bone density and ligamentous calcification. These patients presented several difficult orthopaedic problems. Two brothers with hypophosphataemic vitamin D-resistant osteomalacia presented with bone pains, muscle weakness, limitation of motion in the back and height loss. Treatment with oral phosphate supplements in addition to high doses of Vitamin D2 was dramatic, with complete disappearance of muscle weakness and bone pain.