In four patients with acute neurologic deficits non-enhanced CT on admission showed a hyperdense segment of one middle cerebral artery. These patients eventually turned out to have complete infarctions of the middle cerebral artery territory, the high density representing an intravascular clot. Three patients died within a few days and one survived with disabling deficits, so this visualisation of emboli on CT may be considered to be a sign of a poor prognosis.