A case of adult onset hypophosphatemic vitamin D resistant osteomalacia is described. A 40-year-old female who complained of thorax and lumbar pain and gait disturbance was admitted to our hospital on 7 November, 1988. The patient had hypophosphatemia with normal plasma calcium, parathyroid hormone and 25-hydroxy vitamin D"3 concentrations, but had decreased tubular reabsorption of phosphate and decreased plasma 1, 25-dihydroxy vitamin D 3 concentrations. The iliac crest bone biopsy showed osteomalacic changes. The 99m Tc-MDP bone scintigram showed evidence of increased bone turnover with raised plasma alkaline phosphatase concentrations. After treatment with oral 1 α-hydroxy vitamin D%D3 (3-6 μg/day) and intravenous or oral phosphate supplement (0.47-1.74 g/day), the subjective and clinical findings improved.