Huntington's disease (HD) is attributed to a triplet CAG repeat mutation, and about half of the variation in onset age can be explained by the size of the repeat expansion. Recently, a TAA repeat polymorphism in close linkage to the kainate receptor, GluR6, was reported related to onset age in HD. We examined this polymorphism in 258 unrelated HD-affected persons (172 from a clinic sample and 86 from a postmortem series). This study confirms that the 155 allele is associated with younger onset age of HD and suggests that it is in linkage disequilibrium with a variant of the GluR6 gene or another gene in this region.