We retrospectively reviewed the cranial MRI appearances of 25 patients with AIDS and microbiologically proven central nervous system (CNS) cryptococcosis. Four patients had a normal scan. Ten patients had dilated perivascular Virchow-Robin spaces that were hyperintense on T2-weighted images. Nine of these patients developed progressive cryptococcomas, eight in the basal ganglia and one in the cerebral white matter. The cryptococcomas displayed high signal on T2-weighted and intermediate to low signal on T1-weighted images. None enhanced after dimeglumine gadopentetate. No abnormal dural or leptomeningeal enhancement was detected in any patient. One patient developed an acquired arachnoid cyst during treatment of CNS cryptococcosis which was thought to represent a focal collection of organisms and mucoid material within the subarachnoid space. In addition either cerebral atrophy and/or background white matter hyperintensity on T2-weighted images was present in 19/25 patients. In two patients the neuropathological findings at autopsy correlated well with the imaging abnormalities. In conclusion, this spectrum of MRI appearances in CNS cryptococcosis reflects the pathological mechanism of invasion by the fungus, but a normal scan or one with features of CNS HIV infection such as atrophy or white matter hyperintensity does not exclude the diagnosis. © 1996 The Royal College of Radiologists.