The present study aims at estimating the total cost of MS in Europe based on actual cost data from nine countries and published epidemiological evidence. The epidemiological data are reported as 12 months prevalence estimates and cost data calculated as annual cost per patient at given levels of disease severity. Cost data are extrapolated to the rest of Europe based on a model, using economic indexes adjusting for price level differences in different sectors between countries. The aggregated annual cost estimates are presented in Euro for 2005. In 28 European countries with a population of 466 million, an estimated 380 000 individuals are affected by MS. The total annual cost of MS in Europe is estimated at 12.5 billion in year 2005, corresponding to a cost of 27 per European inhabitant. Direct costs represent slightly more than half of the total cost (6.0 billion). Informal care is estimated at 3.2 billion, and indirect costs due to morbidity at 3.2 billion. Thus, the largest component of costs is found outside the formal health care sector. Although our model appears to predict costs reasonably well, when comparing to previous national studies not included in the estimates, there are considerable uncertainties when extrapolating cost data across countries even within Europe. These weaknesses can only be overcome by collecting primary data.