A 52-year-old woman with alcohol abuse presented with recent worsening of vision, imbalance, and confusion. Examination revealed counting fingers acuity in both eyes with central scotomas, color vision loss, horizontal nystagmus, and gait ataxia. Thiamine was initiated as treatment for a presumptive diagnosis of Wernicke encephalopathy (WE). Brain MRI revealed high T2 signal in the dorsal midbrain and thalami characteristic of WE. The lack of optic disc edema, usually present in patients with WE who have severe optic neuropathy, and lack of visual loss reversibility with thiamine treatment, led to the suspicion of coexisting Leber hereditary optic neuropathy (LHON), which was later confirmed when testing revealed the 14484 mitochondrial DNA mutation. Over the ensuing months, vision did not recover despite improvement of other neurologic findings. Irreversible optic neuropathy in WE should prompt consideration of a coexisting mitochondrial disorder such as LHON.