Patients will be followed in the clinic every 3 months for a history, physical examination, X-rays, blood tests, and measurements (weight, head circumference, and bone lengths). Children will receive a 3 to 4 hour infusion of pamidronate through an intravenous catheter (thin flexible tube placed in a vein) once a day for 3 days each visit. (Once inserted, the catheter is left in place to avoid multiple needle sticks for administering the drug and collecting blood samples.) Children who are taking growth hormone will be given the drug at the first treatment visit. At that time, the accompanying parent will be instructed on how to mix the drug and give injections. The child receives an injection 6 days a week (Sunday off).