Eleven patients with primary brain lymphoma and three patients with secondary brain lymphoma were analysed in detail on the results from the CT studies. Almost all the lesions were found in the basal ganglia and periventricular regions. Leptomeningeal lesion was noted only in one case in the three cases with secondary lesions while no such lesions were revealed in the cases with primary lesions. On the contrast studies while almost all the lesions showed homogenous contrast enhancement, the central low density areas in the lesions were seen in the two lesions in the 28 primary lesions (7.1%) and in the one lesion in the 5 secondary lesions (20%). The leptomeningeal spread of the lesion and the more frequent central low density area in the lesion are considered to be the differential points of the secondary brain lymphoma from the primary brain lymphoma.