We describe the case of a 22-year-old female complaining of ophthalmoplegia, which deteriorated with seizure. Leigh syndrome (LS) was diagnosed by identifying the m.9176T>C mutation. She improved with vitamin cocktail therapy plus intravenous methylprednisolone, and had an excellent prognosis. This was the first case of an adult patient with LS presenting with the m.9176T>C mutation and reporting cortical symptoms, which in this case comprised cortical vision loss, and cortical, basal ganglia, and brainstem signal changes on magnetic resonance imaging.