Several lines of evidence implicate CD56(bright) NK cells in the pathogenesis of multiple sclerosis (MS). This proposed immunoregulatory pathway involves already established susceptibility genes such as interleukin-2 receptor alpha (IL2RA) and interleukin-7 receptor (IL7R). We therefore investigated the CD56(bright) NK cell effector molecule KIR2DL4 for its involvement in genetic susceptibility to MS in a study population of 763 cases and 967 controls. Whereas 26% of the study population has a genotype corresponding to a lack of any functional membrane-bound form of the molecule, no association of the KIR2DL4 transmembrane alleles with susceptibility to MS was observed.