Two cases of vitamin D intoxication are presented. The patients, one aged three months, and the other aged four months, were given Vit D in doses ranging from 30,000 IU/day to 60,000 IU/day for over a period of from one to three months. Laboratory data showed serum calcium levels of 17.6-19.5 mg/dl and phosphorus levels of 2.6-3.2 mg/dl. Renal ultrasonographic examination demonstrated medullary nephrocalcinosis in both patients. In this study the clinical, biochemical and ultrasonographic findings and the therapy of Vit D intoxication are reviewed, and preventive measures are suggested.