Primary hyperparathyroidism is rare in adults, but extremely rare in children under the age of 14 years. Childhood hyperparathyroidism usually becomes manifest after 10 years of age and is most frequently caused by a single adenoma. Rarely, the "hungry bone syndrome" develops following surgery. In this case report we would like to present an 11 9/12 year old girl with bilateral genu valgum deformity owing to a single parathyroid adenoma. Furthermore, she developed the "hungry bone syndrome" following parathyroid surgery.