Thirteen patients with a dense appearance of the horizontal part of the middle cerebral artery (MCA) "dense middle cerebral artery sign" in CT scans taken within 24 hours after onset of ischaemic stroke had considerably poorer prognosis than controls with stroke, but without the sign. A hyperdense appearance of the MCA is known to be associated with thromboembolism, but dense middle cerebral artery sign is also an early warning of a large infarction, brain oedema and poor prognosis in infarction in the MCA area.