Infantile hypercalcemia becomes manifest in 15% of patients with Williams syndrome (WS) and generally is not clinically severe. However, some patients with WS can have severe hypercalcemia and do not respond well to traditional therapies. Recently, pamidronate has been used in the treatment of childhood hypercalcemia associated with many disorders, but there is little experience with the treatment of hypercalcemia with bisphosphonates in patients with WS. We present a 17-month-old female patient, who had been diagnosed as WS by genetic analysis, admitted to our clinic for the investigation of severe hypercalcemia (4.02 mmol/L). Because the patient did not respond very well to fluid administration, furosemide infusion, and dietary calcium restriction, pamidronate infusion was performed and calcium levels returned to normal within 2 days. This case report is presented to point out that pamidronate therapy seems to be a safe and efficient way of treating life-threatening hypercalcemia in WS.