A 54 years old man, who had undergone a cystectomy and urinary diversion surgery 31 years previously, complained of progressive generalized bone pain, muscle weakness and walking abnormality for six months. Laboratory investigations revealed elevated alkaline phosphatase, high serum chloride level and metabolic acidosis. Osteomalacia was suspected due to clinical and laboratory findings. Osteomalacia due to hyperchloremic metabolic acidosis is a complication of urinary diversion. Regular monitoring of pH, chloride, bicarbonate, and calcium-phosphorus metabolism is therefore essential for early diagnosis and treatment.