BACKGROUND: Leber's optic neuropathy (LON) is the phenotypic expression of an inherited disorder due to a mitochondrial DNA mutation. Numerous loci of a point mutation in the mitochondrial genome are reported: 3460, 4160, 11778, 14484 and, 15257. Typically visual loss occurs in young males and a positive family history is found. Peripapillary telangiectasias are reported to be diagnostic for the disease and cardiac conduction abnormalities are sometimes present. PATIENTS: We present six patients who lost vision in both eyes with neither family history of visual loss, typical fundus abnormalities, nor cardiac abnormalities. All were initially misdiagnosed as either anterior ischemic optic neuropathy, hereditary optic atrophy, thromboembolic disorder, toxic amblyopia, multiple sclerosis, traumatic optic neuropathy, or complicated papilledema. METHODS AND RESULTS: Diagnosis was possible in all six cases by mitochondrial DNA studies (five patients with 11778, one with 3460). Magnetic resonance imaging using short-time inversion recovery sequences demonstrated in three tested patients a hyperintense signal within the intraorbital portion of the optic nerve, enhancing after Gadolinium infusion. CONCLUSION: Presentation of LON can be atypical, i.e. occurring in a female, at an advanced age, without family history, without retinal telangiectasias, with other fundus findings, or with unilateral visual loss for prolonged period. Diagnosis of LON should be suspected in every patient with atypical visual loss secondary to an optic neuropathy of undetermined etiology and mitochondrial DNA studies should be performed. Magnetic resonance imaging can be helpful in such cases.