A survey of 289 severely retarded inpatients at a school for retarded children in American Fork; Utah revealed 67 patients with osteomalacia as defined by hypocalcemia, hypophosphatemia, elevated serum alkaline phosphatase levels, and appropriate bone changes. Investigation of the variables which might influence bone mineralization revealed no differences in age, sex, physical activity, sunshine exposure, or dietary intake of vitamin D between the osteomalacia and nonosteomalacia groups. However, all of the patients with osteomalacia were receiving anticonvulsant medications, either phenobarbital, diphenylhydantoin, or both. Duration of anticonvulsant therapy was the most important contributing factor to the development of osteomalacia. Seventy-five percent of patients who had received anticonvulsants for more than ten years had osteomalacia. The single most costly medical problem at the school is the treatment of pathologic bone fractures due to demineralized bone.