A possible role of oxidative stress in the pathogenesis of multiple sclerosis (MS) and in experimental autoimmune encephalomyelitis has been suggested. The detoxification enzyme NAD(P)H dehydrogenase, quinone 1 (NQO1) has been found up-regulated in MS lesions. A previous report described an association between the SNP rs1800566 in the NQO1 gene and the risk for MS in the Greek population. The aim of this study was to replicate a possible influence of the. SNP rs1800566 in the NQO1 gene in the risk for MS in the Spanish Caucasian population.We analyzed allelic and genotypic frequency of NQO1 rs1800566 in 290 patients with MS and 310 healthy controls, using TaqMan Assays.NQO1 rs1800566 allelic and genotypic frequencies did not differ significantly between MS patients and controls, and were unrelated with age of onset of MS, gender, and clinical type of MS.Our results indicate that NQO1 rs1800566 does not have an effect on MS disease risk.