Arachnoid cysts which develop in relation to the cerebral hemispheres are usually found in the middle cranial fossa. These cysts are usually asymptomatic but can produce symptoms if there is haemorrhage into the cyst or the development of an associated subdural hematoma. Recent publications have emphasised the association of arachnoid cysts of the middle fossa with subdural haematomas. This report describes a case of an asymptomatic arachnoid cyst which ruptured into the subdural space. This event was followed by the development of symptoms despite the lack of haemorrhage.