Patients with chronic kidney disease on peritoneal dialysis have very low 25-(OH) vitamin D levels. Vitamin D deficiency may be involved in generalized atherosclerosis, vascular calcification and cardiovascular mortality. Among others, Osteoprotegerin (OPG) has been implicated in the pathogenesis leading up vessel calcification in this patients. Furthermore, very low levels of 25-(OH) vitamin D in peritoneal dialysis patients are associated with increased levels of OPG and high values of vascular calcification scores in x-rays.