We encountered a 60-year-old man who had been diagnosed with heart failure of valvular disease and infective endocarditis; he was being treated with intravenous antibiotics and diuretics. On the 12th hospital day, he suddenly lost consciousness; computed tomography showed a right-sided huge subdural hematoma (SDH) with brain herniation. He died after invasive care was discontinued. A massive SDH was noted at autopsy, and microimaging demonstrated ruptured infective arteritis, without aneurysm, on the surface of the culprit lobe. Acute SDH usually occurs after head trauma, but an area of nonsaccular aneurysmal arteritis can also result in acute SDH.