Mycotic aneurysms are rarely seen in patients who have infective endocarditis, and the management of these patients remains controversial. We present the case of a patient who had infective endocarditis complicated by a mycotic aneurysm of the left middle cerebral artery. There was substantial mitral regurgitation, and Streptococcus viridans was isolated from the blood samples. Dysarthria appeared during the 4th week of the antibiotic therapy, but resolved completely 8 hours after onset. The left middle cerebral artery was embolized with platinum detachable coils. On the 7th day after the radiologic intervention, the native mitral valve was replaced with a 33-mm St. Jude Medical® bileaflet mechanical mitral prosthesis. Most mycotic aneurysms show notable regression of symptoms with effective antibiotic treatment, and a very few may diminish in size. However, it is impossible to predict the response of these aneurysms to therapy. To prevent the perioperative rupture of mycotic aneurysms and intracranial hemorrhage, priority should be given to endovascular interventions to treat cerebrovascular aneurysms in patients such as ours.