Primary hyperparathyroidism is a relatively common endocrine disease in which the parathyroid gland(s) produce excessive amounts of parathyroid hormone, leading to high blood calcium levels. Other affected organs include the skeleton and the kidneys. The aim of this study is to characterize primary hyperparathyroidism as it presents today, and to develop a rationale and guidelines for treating patients with this disease. Patients are not randomized to any treatment; rather they are followed and treated according to accepted guidelines. The approach is to follow subjects closely, using history, physical exam, biochemical, bone densitometric and bone histomorphometric techniques. Data will be analyzed by forming groups of subjects, and following relevant indices over time. After three baseline visits (over 1-3 months), patients will be seen over four months unless they undergo parathyroidectomy, in which case follow-up will be twice a year.