Abstract： We report a case of adult-onset dystonia presenting with chronic progressive external ophthalmoplegia. The patient had ptosis in both eyes, particularly the left eye, for no obvious reason since the age of 10, which was progressively aggravated. The clinical diagnosis was chronic progressive external ophthalmoplegia. However, whole gene sequencing revealed the mitochondrial A3796G missense mutation, so the patient was clearly diagnosed as adult-onset dystonia and given treatment to reduce blood glucose and improve muscle metabolism. The A3796G mutation in the ND1 subunit of the mitochondrial complex leading to ophthalmoplegia is relatively rare, requiring a combination with genetic testing for confirmation of diagnosis.