A narrow serum calcium level which is essential for many metabolic processes is regulated by the calcium-sensing receptor which regulates parathyroid hormone (PTH) release. Primary hyperparathyroidism is supposed to be the third most common endocrine disorder. Besides nephrolithiasis and an increased incidence of cardiovascular symptoms it is associated with bone loss and an increased risk of fracture. Several different classical bone turnover markers have been shown to be increased. However, there are many uncertainties in pathophysiology of PHPT. Hardly any conclusive data exist on the RANK (receptor activator of nuclear factor-kB)/RANKL (receptor activator of nuclear factor-kB ligand)/OPG (osteoprotegerin) system, cathepsin K, sclerostin, FGF-23 (Fibroblast growth factor-23), Klotho, and DKK 1 (Dickkopf 1) in patients suffering from PHPT.