At least five mtDNA point mutations appear sufficient in themselves to cause Leber's hereditary optic neuropathy (LHON), while several other base substitutions act synergistically by increasing the risk for optic atrophy. The three most common mutations associated with LHON are ND4/11778, ND1/3460 and ND6/14484 covering 50, 30 and 10% of the families, respectively. mtDNA heteroplasmy is seen most often in sporadic cases reflecting a recent mutational event. The etiology of LHON is still enigmatic. In addition to mtDNA mutations, nuclear gene interaction and environmental factors may contribute to the expression of optic atrophy.