Giant aneurysms of the anterior communicating artery (AComA) are rare. The clinical presentation of giant AComA aneurysms is usually associated with the mass effect of the space-occupying lesion or with subarachnoid haemorrhage. A giant AComA aneurysm presenting with a seizure has only been reported twice previously. We report a 70-year-old female patient, in whom a single seizure was the only symptom of a giant AcomA aneurysm, with no neurological deficit. The diagnosis of unruptured giant AComA aneurysm was made with cranial CT, MRI and angiography. The patient refused surgical intervention, was treated with anti-epileptic therapy and has been asymptomatic for 7 months. We suggest that elderly patients presenting with a first seizure need detailed evaluation and giant aneurysms, which may be confused with other intracranial space-occupying lesions, need to be considered in the differential diagnosis. (C) 2006 Elsevier Ltd. All rights reserved.