We are investigating genetic association to Multiple Sclerosis (MS) and different measures of severity of MS. We are also investigating the interaction between genetic variants associated with MS and lifestyle exposures. The most important genetic region for MS susceptibility is the HLA region on chromosome 6. We plan to impute MHC class I and class II HLA alelles using genotypes from SNP arrays in patients and controls from Sweden and a Swedish reference panel generated in the SweGen project as well as in the EIMS project. We will then investigate association of HLA alleles to MS and severity of MS as well the interaction of HLA with other risk factors.