The contribution of intravenous contrast medium to the final diagnosis was assessed in 300 patients undergoing routine axial computed tomography (CT) of the brain. Two-hundred-and-twelve patients presented with symptoms or signs suggesting focal intracranial pathology and 88 with non-focal features. A total of 110 post-contrast scans were abnormal. The differential diagnosis was altered in 15 patients (5%) following contrast enhancement, 13 of whom presented with focal symptoms and signs. In three patients with normal plain scans and symptoms and signs suggesting focal intracranial pathology abnormalities were only seen after contrast medium and in only one was the lesion surgically treatable. In a further 15 patients (5%) contrast enhancement increased the certainty of the diagnosis that had been made on the uncontrasted scan. We feel that when the uncontrasted scan is normal contrast enhancement is only helpful in a limited number of patients with symptoms and signs suggesting focal intracranial pathology. Contrast enhancement is still important in differentiating abnormalities seen on the unenhanced scan even with modern high resolution CT scanners.