In this study, we compared three different therapy modes (150,000 IU, 300,000 IU, and 600,000 IU vitamin D p.o.) in infants with nutritional vitamin D deficiency rickets (VDR). Our purpose was to determine the most effective dosage of vitamin D with least side effects for treating VDR. The study included 56 patients, 3-36 months of age, with nutritional VDR and 20 age-matched control infants. In all infants, serum calcium, phosphorus, alkaline phosphatase, magnesium, serum 25-hydroxycholecalciferol, plasma intact parathormone levels and urinary Ca/creatine ratio were determined. Of 56 patients, 52 were able to be followed long-term. These patients were reexamined on the 3(rd) day, 7-10(th) day, and 25-30(th) day after treatment. On the 30(th) day post-treatment, we did not find any difference between the doses in the improvement of rickets. However, hypercalcemia was present in eight infants who had been administered 300,000 IU (two infants) and 600,000 IU (six infants) of vitamin D. In conclusion, our findings showed that 150,000 IU or 300,000 IU of vitamin D was adequate in the treatment of VDR, but 600,000 IU of vitamin D may carry the risk of hypercalcemia.