We report a case of urolithiasis in a patient with idiopathic hypoparathyroidism treated with vitamin D therapy. A 30-year-old woman with idiopathic hypoparathyroidism, who had been treated with vitamin D therapy with 2-4 micrograms/day of alpha-calcidol for 9 years, was admitted for recurrence of bilateral renal stones and progressing left hydronephrosis. Laboratory data revealed normal serum calcium level and remarkable hypercalciuria. The dose of oral administration of alpha-calcidol was reduced to 1 microgram/day and 2 mg/day of trichlormethiazide was started. Now her serum calcium concentration and the total amount of urine calcium was completely under control. Bilateral renal stones are no longer progressive and tetany has not been recognized. We considered it essential to monitor closely not only the serum but also the urine calcium level in the vitamin D therapy for idiopathic hypoparathyroidism.