We report a fifty three year old man who presented with progressive visual loss. Investigation disclosed a giant aneurysm with optic nerve compression, which was successfully treated surgically. The patient had typical skin lesions of tuberous sclerosis, but did not suffer from a seizure disorder or mental retardation. In the past he had had an enucleation for glaucoma secondary to a retinal phakoma. Cerebral aneurysms are discussed in relation to the tuberous sclerosis disease process. After review of the literature, we propose that the aneurysms are secondary to dysplastic change in the vessel walls, this is in keeping with the abnormal tissue proliferations in this disease.