A 26 year old man ran a distance of 11/2 miles in 12 minutes. Soon after this effort he developed visual disturbances in the right field of vision and left-sided clumsiness associated with left frontal headache, nausea and vomiting. Four vessel arteriography and skull x-rays were normal but examination of the visual fields showed a right superior quadrantic field defect and the electroencephalogram a left posterior temporal slow focus. EMI scan performed a few days later showed an infarct in the left inferior occipital pole. No known risk factors for stroke were present. It is suggested that the cerebral infarction associated with headache was related to effort at altitude and most importantly to lack of physical training.