We present a 16 month-old previously healthy boy with refractory hypercalcemia due to an overdose of an over-the-counter vitamin supplement. The patient presented to the emergency department with a few weeks' history of irritability, constipation and intermittent vomiting. His serum calcium was found to be 18 mg/dl. He was first treated with intravenous fluids, furosemide and glucocorticoids without significant improvement, but became eucalcemic within 24 hours after receiving a single dose of pamidronate. This case highlights the potential danger of high dose vitamin supplements in children, and the salutary effects of treatment with bisphosphonate.