Spontaneous complete thrombosis of an unruptured intracranial aneurysm leading to ischemic stroke is rare. We present a case of a 56-year-old man who suffered an acute left middle cerebral artery (MCA) infarction, attributable to complete thrombosis of an unruptured saccular MCA bifurcation aneurysm with occlusion of the parent artery. The presenting hemiparesis and aphasia partially improved over a long hospital rehabilitation stay. Follow-up imaging demonstrated no recanalization of the aneurysm or parent vessels. To the best of our knowledge this is the first documented case of isolated MCA territory infarction due to complete spontaneous thrombosis of a saccular aneurysm.