The usefulness of brain scans for detecting unsuspected cerebral metastases in patients with carcinoma of the lung was studied in a group of 35 such patients who had routine brain scans as part of the initial evaluation. Seven (20%) had scans that were positive for tumor, but of these 7 had neurologic deficits corresponding to the brain scan abnormality. Routine brain scans for evaluation of carcinoma of the lung are not justified if neurologic examination is normal.