This study assessed with a neuropsychological battery the outcome of 27 patients operated on for an aneurysm of the Middle Cerebral Artery a mean of 35 months before, and of 27 patients operated for aneurysms of the Posterior Communicating Artery, a mean of 47 months before. Both groups showed a defective pattern of performance that was related to the hemispheric side of the aneurysm with left-sided patients impaired on naming, verbal fluency and verbal short-term memory and right sided patients on both short-term and long-term spatial memory and discrimination of line orientation. In single cases, the scope of neuropsychological impairment was sometimes wider than that expected only on the basis of the competence of the affected hemisphere.