In order to determine whether normal height is possible in persons with vitamin D-resistant rickets, treatment should begin in infancy, since characteristic leg deformities and short stature are a result of weight bearing on the softened bones. Early treatment depends upon the discovery of hypophosphatemia in the neonatal period. A 19-month-old boy with familial hypophosphatemic vitamin D-resistant rickets, who received adequate vitamin D therapy starting at age 3 months, now shows no physical manifestations of rickets and is of normal height. In his mother and grandmother, the diagnosis was made and therapy attempted at 12 and 46 years, respectively. Typical rachitic findings, including shortness of stature, are permanently present in them.