BACKGROUND : Thrombosed cerebral aneurysm (TCA) can cause cerebral infarction. However, treatment of cerebral infarction due to embolism from TCA is controversial because of the risk of rupture, and no consensus has been established for the treatment of patients with this condition. METHODS : A 75-year-old woman suffered left hemiparesis. Computed tomography (CT) showed a high-density round mass in the right sylvian fissure, which was suspected to be a nonruptured TCA. Magnetic resonance (MR) angiography and CT angiography demonstrated an aneurysm in the distal part of the right middle cerebral artery with poor opacification of most of the aneurysm, suggesting partial thrombosis. Diffusion-weighted MR imaging revealed high intensity in the right frontal lobe, in a distribution distal to the aneurysm. The diagnosis was cerebral infarction due to embolism from a partially thrombosed aneurysm. She was treated with antithrombotic therapy. On day 4, she suddenly became comatose. CT and CT angiography revealed subarachnoid hemorrhage (SAH) and enlarged opacification in the aneurysm, respectively. She underwent neck clipping of the aneurysm, but her neurologic improvement was poor. TCA causing ischemic stroke followed by SAH is extremely rare, with only 4 previous reported cases. All patients had received antithrombotic therapies, and most aneurysms had ruptured within a few days after starting antithrombotic therapy. The outcomes were extremely poor. CONCLUSIONS : We suggest that antithrombotic therapy might be avoided for these patients. Early surgical treatment without antithrombotic therapy is recommended to prevent aneurysm rupture and recurrent distal embolism from the TCA.