This chapter considers the basic anatomy and physiology of the parathyroid gland, followed by its pathologies and their implications for anaesthesia. There are usually two pairs of parathyroid gland, superior and inferior, each measuring 4 x 2 x 6 mm, surrounded by fat and each weighing approximately 25-40 mg. About 80-90% of patients have four parathyroids. Parathyroid hormone is secreted by the parathyroid chief cells in response to the fall in the level of circulating, free calcium. The clinical presentation of primary hyperparathyroidism has altered over the past century. It is a commonly recognised endocrine disorder, with the number of parathyroidectomies increasing each year. The gold standard of treatment and the only hope of cure is surgical parathyroidectomy. Preoperative intravenous infusion of methylene blue is used to identify the parathyroid glands, and in open or minimally invasive surgery the operative times can be reduced.