A 9-year-old boy, who had been admitted to the Pediatric Department for the examination of IgA nephropathy, was transferred to our urological clinic on Aug. 6, 1985, because of parathyroid crisis. Before urological consultation, he had been complaining of bilateral knee and calcaneal pain, anorexia and abdominal pain, which had persisted for several days. Laboratory data indicated serum Ca of 17.6 mg/dl, iP of 2.3 mg/dl and iPTH of 0.77 ng/ml. Roentgenographic examination such as chest, extremities and neck computed tomography showed no abnormal findings. The final diagnosis was parathyroid crisis caused by primary hyperparathyroidism and neck exploration was carried out on August. 10. Left upper parathyroid gland, which was 1 cm in diameter, was surgically removed. The other three glands were normal in size. Histological examination of the resected parathyroid gland revealed chief cell adenoma. In the post-operative course, serum Ca level was soon reduced to the normal range and bone pain disappeared rapidly. During the follow up period of 2.5 years, the patient was clinically free of recurrence. Only 23 cases of primary hyperparathyroidism in children have been reported in the Japanese literature. The clinical characteristics of these specific cases are that primary hyperparathyroidism in children shows a low incidence of renal lesion, but the complicated bone disease is of higher incidence compared with the adult cases. Histopathologically, parathyroid adenoma was frequently observed (14/19), and the other 5 cases were parathyroid hyperplasia.