A 46-year-old female patient with previously recognized Graves' ophthalmopathy, underwent total thyroidectomy. After thyroid surgery exophthalmos worsened and signs unsteadiness of gait appeared. Magnetic resonance imaging showed a lesion in the basal portion of the left cerebellar hemisphere. Therefore, the patient underwent surgery. Pathological examination revealed dysplastic gangliocytoma of the cerebellum (Lhermitte-Duclos disease).