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The patient was a 41-year-old man with a history of diabetes mellitus since the age of 22 years and a family history of diabetes in his mother. He had repeated headaches, cerebellar symptoms, and bilateral cerebellar lesions on brain MRI (DWI, T₂ FLAIR hyperintensities). He was previously diagnosed with cerebellitis and treated with steroids at another hospital. Upon his third relapse, he was referred to our department. Clinical findings included short stature, diabetes, elevated CSF lactate and pyruvate levels, and increased lactate levels on aerobic exercise testing. Muscle biopsy revealed mitochondrial pathological abnormalities, and genetic testing of muscle tissue identified the mitochondrial DNA m.3243 mutation. These findings led to the diagnosis of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). Stroke-like lesions in MELAS can involve not only the cerebrum but also the cerebellum. When cortical-predominant lesions with associated vascular dilatation are observed, MELAS should be considered in the differential diagnosis.