Objective: To study the clinical features and causes of postoperative brainstem and cerebellar infarcts. Methods: Two groups were studied. The 10 group 1 patients had cardiac (eight) or aortic (two) surgery. The 12 group 2 patients had noncardiac-nonvascular surgery, including orthopedic (five), gynecologic (four), and general (three). Patients were studied by stroke services at university hospitals in Boston (13), Charlottesville (three), Baltimore (three), and Mainz (three) during 2 consecutive years. Results: Onset of strokes was immediately postoperative (six), during the first 48 postoperative hours (nine), and delayed 3 days or more (seven). Clinical syndromes were altered level of consciousness or cognition (151, vestibulocerebellar (four), and hemiparesis with focal brainstem signs (three). Infarction involved the brainstem (131, cerebellum (131, and posterior cerebral artery hemispheric territory (10). Causes: In group 1, five infarcts were due to cardiogenic embolism and three to embolism from the aorta. One patient had a postoperative pontine lacunar infarct and one developed an infarct in the territory of a known stenotic basilar artery. In group 2, one patient had vertebral artery injury from instrumentation, one had medical complications with severe hemorrhage and hypotension, and 10 most likely had position-related vertebral artery thromboses. Conclusions: Patients with postoperative brainstem and cerebellar infarcts present with altered consciousness or vestibulocerebellar syndromes. The major cause of brain infarcts after cardiac surgery is embolism from the heart and aorta. The causes of infarction after general surgery are less clear, but neck positioning during or after surgery may play an important role by promoting thrombi in compressed arteries that later embolize intracranially when neck motion becomes free.