Malignant lymphoma of the central nervous system has been found more and more often in recent years, partly because of the increased use of radiation and such drugs as steroids and antibiotics. However, the definite diagnosis of this disease is difficult until histological verification has been done by operation or autopsy. Since the revolutionary development of computed tomography, however, several reports have been presented, on the computed tomography of malignant lymphoma of the thorax and abdomen. Nevertheless, only a few cases of intracranial malignant lymphoma have been reported. The purpose of this paper, using four patients, is to emphasize the value of computed tomography in the diagnosis of intracranial malignant lymphoma. The characteristic CT findings of intracranial malignant lymphoma may be summarized follows: (1) the tumors are demonstrated to be well-defined, nodular-shaped, and homogenous isodensity - or slightly high-density - lesions in plain scans, and the tumors homogenously increase in density upon contrast enhancement; (2) the disease always has multifocal intracranial lesions, which are shown simultaneously or one after another, and (3) perifocal edema is prominent around the tumors in the cerebral hemisphere.