Aneurysms at the distal branch of the middle cerebral artery may be mycotic or congenital in origin. A 34 year-old male patient was admitted with a seizure and a 7-day history of upper respiratory tract infection. The neurological examination showed no abnormality except for headache and mild dysarthria. There was no intracardiac lesion suggesting infective endocarditis. CT, MRI and cerebral angiograms revealed a partially thrombosed giant aneurysm at the distal branch of the middle cerebral artery. Pathologic examination revealed acute inflammatory cells and focal necrosis in the aneurysmal wall as well as recent thrombus. Here, we are reporting an unusual case with a giant distal middle cerebral artery aneurysm with intramural inflammation, suggesting a congenital giant aneurysm with secondary infectious inflammation.