PURPOSE: Vitamin D deficiency is often detected during metabolic evaluation in the nephrolithiasis population. Multiple vitamin D repletion protocols exist, although their differing impact on urinary stone formation risk factors is unclear. MATERIALS AND METHODS: Patients with a history of calcium stones and vitamin D deficiency (less than 30 ng/ml) were randomized to receive either 1,000 IU daily or 50,000 IU weekly of vitamin D supplementation for 6 weeks. Patients completed a pretreatment and posttreatment serum vitamin D level evaluation and 24-hour urine collections to assess the response and any changes in urine stone formation risk parameters. RESULTS: A total of 21 patients completed the study, including 8 who received 1,000 IU daily and 13 who received 50,000 IU weekly. The 50,000 IU weekly group showed a significant increase in median serum vitamin D levels of 23 ng/ml (135%, p <0.01), while the 1,000 IU daily group showed a nonsignificant median increase of 9 ng/ml (49%, p = 0.12). Post-repletion 24-hour urine analysis demonstrated no significant change in urine calcium between the groups, including a median change of -11 mg (IQR -143-29) in patients receiving 1,000 IU and -16 mg (IQR -42-66) in those receiving 50,000 IU. Between the groups there was no significant difference in the supersaturation of calcium oxalate or calcium phosphate. CONCLUSIONS: High dose and low dose vitamin D repletion had no effect on urine calcium excretion or the supersaturation of calcium salts in known stone formers. The higher dosing regimen, which had superior repletion, may be the optimal protocol in patients with vitamin D deficiency.