A 26-year-old woman developed a sudden headache, ptosis, and diplopia. Magnetic resonance imaging and angiography demonstrated a symmetrical lesion from the midbrain to the brainstem, involving the solitary nucleus and multifocal cerebral artery narrowing. Reversible cerebral vasospasm syndrome (RCVS) was suspected, and the patient improved after vasodilatation. Leigh syndrome was suspected due to the elevated serum lactate levels, so mitochondrial DNA was analyzed, and an m.9176 T>C mutation was detected. The final diagnosis was adult-onset Leigh syndrome manifesting as RCVS. An uncontrolled baroreflex due to a solitary nuclear lesion or endothelial dysfunction may have contributed to her unique presentation.