Primary hyperparathyroidism (PHPT) is characterized most commonly now as an asymptomatic disorder with hypercalcaemia and elevated levels of parathyroid hormone (PTH). The elevation in PTH is detected by both the standard immunoradiometric assays (IRMA) and a more recent IRMA that detects only the 1-84 full-length PTH molecule. The serum calcium concentration is usually <1 mg dL(-1) above normal. Recently, another variant of PHPT (normocalcaemic PHPT) has been described in which the serum calcium is normal but the serum PTH is elevated, in the absence of any secondary cause for PTH elevation. Although usually sporadic, PHPT also occurs in inherited syndromes. Skeletal manifestations are appreciated by densitometry showing a typical pattern in which cancellous bone of the lumbar spine is reasonably well preserved whilst the cortical bone of the distal third of the radius is preferentially reduced. Although reduced in incidence, renal stones remain the most common overt complication of PHPT. Other organs are theoretical targets of PHPT such as the neurobehavioural axis and the cardiovascular system. Vitamin D looms as an important determinant of the activity of the PHPT state. The 2002 NIH Workshop on asymptomatic PHPT has led to revised guidelines to help doctors determine who is best advised to have parathyroid surgery and who can be safely followed without surgery. New information about the natural history of PHPT in those who did not undergo surgery has helped to define more precisely who is at-risk for complications. At the NIH workshop, a number of items were highlighted for further investigation such as pharmacological approaches to controlling hypercalcaemia, elevated PTH levels and maintaining bone density.