Primary hyperparathyroidism is no longer the severe disorder of ‘stones, bones, and groans’ described by Fuller Albright and others in the 1930s (1,2). Osteitis fibrosa cystica, with its brown tumours of the long bones, subperiosteal bone resorption, distal tapering of the clavicles and phalanges, and ‘salt-and-pepper’ appearance of erosions of the skull on radiograph is rare, and kidney stones are seen in only 20% of patients. Asymptomatic disease is the rule in the vast majority of patients, with the diagnosis commonly following the finding of hypercalcaemia on routine serum chemistry analysis (Table 4.3.1) (3–5). Primary hyperparathyroidism is due to a solitary parathyroid adenoma in 80% of patients (5). Most cases are sporadic, although some are associated with a history of neck irradiation, or prolonged use of lithium therapy for bipolar disease (6, 7). Multiple parathyroid adenomas have been reported in 2 to 4% of cases (8). Parathyroid adenomas can be discovered in many unexpected anatomic locations, including within the thyroid gland, the superior mediastinum, and within the thymus. Occasionally, the adenoma may ultimately be identified in the retroesophageal space, the pharynx, the lateral neck, and even the alimentary submucosa of the oesophagus (9). In approximately 15% of patients with primary hyperparathyroidism, all four parathyroid glands are involved. There are no clinical features that differentiate single versus multiglandular disease. In nearly one-half of cases, four-gland disease is associated with a familial hereditary syndrome, such as multiple endocrine neoplasia 1 (MEN 1) or MEN 2a.