A number of association studies have explored the relationship between the CCR5-Delta32 allele and the risk of developing multiple sclerosis (MS), with varying results. In light of the results of several studies that have analyzed the role of the allele in MS, it has been proposed that the allele is involved in the etiopathogeny of the disease. Our study revealed a statistically significant difference between the study group and the control group for the carriers of at least one deleted allele (P = 0.027). The allele was more frequent in the control group, which suggests a possible protective effect of this deletion against MS. When ethnic origin was taken into account in the same analysis, we saw that the bulk of the difference was attributable to the Basque group, although the trend was also visible in the control group. Consideration of ethnic origin is therefore essential for the analysis of our sample. CCR5-Delta32 allele distribution was higher in the Basque control population than in the Basque MS population, which suggests that it confers a protective effect against MS. Relevant values were a P value of 0.008 and an odds ratio of 0.168 (95% confidence interval, 0.038 to 0.737).