Leigh syndrome is a mitochondrial disease of infancy and early childhood and is rare in adults. We report an autopsy case of adult Leigh syndrome of 15 years duration in a 32‐year‐old man with a familial history of the disease. His initial symptom was clumsiness followed by dullness, and dysphasia and dysarthria appeared in the last 3 months. His brother had similar symptoms and died at the age of 27 years. His sister is also demented. Cranial MRI revealed abnormal signals in the bilateral putamen and tegmentum of the brainstem. Neuropathologically, there were symmetrical, well‐demarcated necrotizing lesions with proliferation of capillaries in the putamen, caudate nucleus and thalamus, as well as in the periaqueductal gray matter of the midbrain and tegmentum of the pons. It seems that the lesions in the putamen were more severe and older than those of the brainstem, the latter having numerous macrophage infiltrations. Neuronal loss and gliosis were also observed in the substantia nigra and cerebellar cortex. This is the first autopsy‐confirmed familial adult Leigh syndrome in China. The clinicopathological features are presented together with a literature review.