OBJECTIVE: To assess the cost-effectiveness of switching patients from atorvastatin (ATV), simvastatin (SIM) or pravastatin (PRA) to rosuvastatin (Crestor(r); RSV), from the perspective of a UK primary Health care provider. METHODS: The clinical benefit assessed was the proportion of patients treated to the European Atherosclerosis Society low-density lipoprotein cholesterol (LDL-C) goal (<3mmol/L). Clinical data were taken from Measuring Effective Reductions in Cholesterol Using Rosuvastatin therapY I (MERCURY I) trial in which 3140 adults with, or at risk of, coronary heart disease initially received a fixed daily dose of RSV 10 mg, ATV 10 or 20mg, PRA 40mg or SIM 20mg. After 8 weeks' treatment, patients were randomised to remain on treatment or to switch treatments as follows: from ATV 10mg, SIM 20mg, PRA 40mg to RSV 10mg or from ATV 20mg to RSV 10 or 20mg for a further 8 weeks. In a decision-analysis model, it was assumed that patients not achieving goal on an alternative statin after 8 weeks would be switched to RSV. Costs for drug acquisition, primary care physician visits, nurse visits and laboratory tests were included where appropriate. Cost-effectiveness was expressed as the cost per patient treated to LDL-C goal over a 16-week period. RESULTS: Initiating and maintaining patients on RSV was more cost-effective than either 1) initiating and maintaining on another statin; or 2) switching from another statin to RSV 10mg. Compared with continuing on ATV, PRA or SIM, switching to RSV would treat more patients to goal at an incremental cost of €17-117 per extra patient treated to goal. CONCLUSIONS: Initiating and maintaining patients on RSV were more cost-effective than switching from the other statins to RSV. For patients intially receiving other statins, switching to RSV treated more patients to goal at relatively little additional total cost while drug costs were equivalent or lower.