Eligible patients will be randomly divided into 2 equal groups depending on whether they will receive vitamin D replacement or not. Randomization will be done using a computer-based random number generator. Patients will receive vitamin D3 tablets 10.000 IU twice a week for 8 weeks followed by a maintenance dose of 1.000 IU daily for 21 months. All patients will be subjected to full history taking and clinical examinations, urinalysis and culture when indicated, liver function tests, urea and creatinine, ionized normalized calcium, phosphate, magnesium, uric acid, potassium, PTH, TSH and both forms of vitamin D [25(OH)D and 1, 25 (OH)2D], low dose CT scan to confirm stone free status and baseline bone density scan, together with metabolic stone workup consisting of stone analysis and two 24-hour urine collections for calculation of volume, osmolality, pH, creatinine, urea, calcium, phosphate, chloride, magnesium, sodium, potassium, oxalate, citrate, uric acid, and quantitative cystine. Similar follow-up measures will be done at 3, 6, 12, 18 & 24 months. At the end of the study, low dose CT scan and bone density scans will be repeated.