There is an association between Leber's hereditary optic neuropathy (LHON) and a multiple sclerosis-like illness, raising the possibility of autoimmune pathogenetic mechanisms in LHON. We therefore investigated the frequency of HLA-DR genotypes in members of 79 families with LHON, defined by the presence of a pathogenic mitochondrial DNA mutation. There was no association between LHON and any HLA-DR genotype. Furthermore, affected relative pairs did not share HLA genotypes more than discordant pairs. We conclude that the HLA-DR locus is not a major genetic determinant for the development of blindness in LHON.