We report a 54-year-old man with osteomalacia due to a bladder reconstruction performed 35 years previously. He had had slowly progressive chest and back pain for 18 months. Osteomalacia due to metabolic acidosis was suspected based on hyperalkalinephosphatasemia and a high serum chloride level, and the diagnosis was confirmed by bone scintigraphy. His symptoms and blood electrolyte levels were improved by oral medication, including sodium hydrogen carbonate. Measurement of the serum chloride level is simple and useful for evaluating acidosis, for which a regular blood test is essential in patients who have undergone bladder reconstruction.