Central nervous system (CNS) manifestations in acquired immunodeficiency syndrome (AIDS) patients are an earlyand common feature. The spectrum of AIDS-related CNS diseases are encephalitis caused by the humanimmunodeficiency virus(HIV) itself, opportunistic infection, infarct and malignancy. We experienced two cases ofCNS involvement in AIDS and they were serologically diagnosed as HIV encephalitis and CNS toxoplasmosis, respectively. In the case of the HIV encephalitis patient, brain MRI showed a non-enhancing lesion with highsignal intensity on T2WI and low signal on T1WI and there was no mass effect on the right frontal lobe, periventricular white matter, splenium of the corpus callosum or bilateral basal ganglia. In the other case of CNStoxoplasmosis, MR showed multiple nodular and rim enhanced mass lesions in the right basal ganglia, thalamus andperiventricular white matter, which were of low signal intensity on T1WI and of high intensity on T2WI. We thusreport the related MRI findings.