Lhermitte-Duclos disease is a rare hamartomatous lesion of the cerebellar cortex that may occur in the setting of Cowden's syndrome, an autosomal dominant condition characterised by multiple hamartomas and neoplastic lesions in skin and internal organs. We add a further case to this rare entity. A 55-year-old female presented with a 3-month history of progressive headaches occasionally associated with nausea and vomiting. Magnetic resonance imaging revealed the presence of a well-defined lesion with an abnormal laminated pattern of cortical architecture involving most of the left cerebellar hemisphere and compressing the fourth ventricle. Complete removal of the cerebellar lesion was performed and histopathological diagnosis verified Lhermitte-Duclos disease. The associated skin lesions and the patients past history of tumors were sufficient for the final diagnosis of Cowden's syndrome. Accurate preoperative diagnosis of Lhermitte-Duclos disease can be made on the characteristic magnetic resonance imaging appearances. It is important to be aware of the link between Lhermitte-Duclos disease and Cowden's syndrome so that appropriate tumor surveillance can be undertaken by the treating physician.