The brain scan has become a safe, efficient, and accurate method of screening patients who are suspected of having intracranial abnormalities. Tumor detection and localization are now possible in approximately 90% of patients seen, comparing favorably with results of angiography and pneumoencephalography. Improvements in radionuclides and detection equipment have made possible refinements of techniques to allow study of cerebral vasculature a t the time of nuclide injection for the routine static studies. Certain tumors have been found to have specific characteristics on the dynamic and static brain scans and can be predicted with some certainty in many instances. Normal scan anatomy and the various histologic tumor types and their patterns are described.