Primary malignant lymphoma of the brain is a rare lesion characterized clinically by varied nonspecific neurologic deficits and usually a rapid fulminant deterioration and death. This course may be altered by radiotherapy, and early diagnosis assumes major importance. Laboratory tests. KEG. radionuclide scans, angiography, and pneumoencephalography may not show definite abnormality in the early stages. This report concerns four cases in which good correlation between the location of the brain lesion and the abnormality on computed tomography scan was demonstrated. © Raven Press, New York.