A randomised double blind clinical trial, accepted by the Medical Products Agency and registered in the European Clinical Trials Database. Aims to evaluate the prevalence of vitamin D deficiency in a pHPT population in relation to gender and age, the correlation between vitamin D status, pre- and postoperative parathyroid hormone level and bone density and the correlation between vitamin D status, metabolic, cardiovascular risk factors and QoL aspects before and after parathyroid adenomectomy.