To illustrate investigations leading to the diagnosis and management of PTH related hypercalcaemia, we present a selection of distinct cases of hypercalcaemia arising from eutopic and ectopic parathyroid adenomas, as well as a case with a syndromic form of PHPT, and a case with FHH type 1 due to a CASR inactivating mutation. This evidence concerns the gene PTH and parathyroid gland adenoma.