BACKGROUND: Chronic kidney disease-mineral and bone disorders (CKD-MBD) are important complications of CKD5D patients that are associated with mortality.METHODS: COSMOS is a multicentre, open cohort, prospective, observational 3-year study carried out in haemodialysis patients from 20 European countries during 2005-07. The present article describes the main characteristics of the European dialysis population, the current practice for the prevention, diagnosis and treatment of secondary hyperparathyroidism and the differences across different European regions.RESULTS: The haemodialysis population in Europe is an aged population (mean age 64.8±14.2 years) with a high prevalence of diabetes (29.5%) and cardiovascular disease (76.0%), and 28.7% of patients have been on haemodialysis more than 5 years. Patients from the former Eastern countries are younger (59.3±14.3 versus 66.0±13.9), having a lower proportion of diabetics (24.1 versus 30.7%). There were relevant differences in the frequency of measurement of the main CKD-MBD biochemical parameters [Ca, P and parathyroid hormone (PTH)] and the Eastern countries showed a poorer control of these biochemical parameters (K/DOQI and K/DIGO targets). Overall, 48.0% of the haemodialysis patients received active vitamin D treatment. Calcitriol use doubled that of alfacalcidiol in the Mediterranean countries, whereas the opposite was found in the non-Mediterranean countries. The criteria followed to perform parathyroidectomy were different across Europe. In the Mediterranean countries, the level of serum PTH considered to perform parathyroidectomy was higher than in non-Mediterranean countries; as a result, in the latter, more parathyroidectomies were performed in the year previous to inclusion to COSMOS.CONCLUSIONS: The COSMOS baseline results show important differences across Europe in the management of CKD-MBD.