Leber's hereditary optic neuropathy (LHON) is a maternally transmitted disease causing acute or subacute, bilateral optic atrophy mainly in young men. It is found to be a mitochondrial disorder with the primary mitochondrial DNA (mtDNA) mutations at 11778, 3460, and 14484. The incidence of each mutation is reported to be race-dependent. Point mutations at mtDNA nucleotide position 11778 and 14484 have been reported in Korean patients with LHON, however there has been no report of mtDNA mutation at nucleotide position 3460. Molecular genetic analyses at four primary sites (11778, 14484, 15257, and 3460) of mitochondrial DNA using the polymerase chain reaction, restriction enzyme digestion, and direct sequencing were performed in a 35-yr-old man with severe visual loss. A point mutation in the mtDNA at nucleotide position 3460 was identified and a conversion of a single alanine to a threonine was confirmed. To our knowledge, this is the first report confirming mtDNA mutation at nucleotide position 3460 in Korean patients with LHON. Detailed molecular analyses would be very helpful for the correct diagnosis of optic neuropathy of unknown etiology and for genetic counseling.