Primary hyperparathyroidism is nowadays not uncommon in Japan. The incidence is considered to be one in every 2,500 to 5,000 persons. Many advances have occurred in diagnosis, localization study, and treatment of the disease. Surgery remains the treatment of choice for patients with primary hyperparathyroidism. Notwithstanding, there are still controversies concerning the management of primary hyperparathyroidism. One of the current disputable points is whether the use of localization study in patients who are undergoing and initial operation is justified or not. Another is whether unilateral exploration is justified or not. The basic reasons for these persistent controversies is the lack of consensus about incidence of multiglandular hyperplasia or double adenomas. Our observation implies that the incidence of hyperplasia or double adenomas among all the patients with primary hyperparathyroidism in Japan is lower than that in western countries. Since diagnostic accuracy of noninvasive localization studies has recently improved, it seems reasonable to adopt unilateral neck exploration in our country. It is also characteristic in Japan that the incidence of parathyroid carcinoma is relatively high (6%) compared with that reported in many other countries.