Previous published series describing the appearances of primary central nervous system lymphoma (PCNSL) state that calcification, haemorrhage and cyst formation are rare, but generally fail to quantify or expand on this statement. We present the pre-treatment computed tomography (CT) findings of 36 patients with biopsy proven PCNSL. In this series, calcification was present in only one very atypical lesion and evidence of haemorrhage was not seen. Small intralesional cysts were present in four of the total of 50 lesions. PCNSL usually appeared as one or more well defined focal lesions, iso- or hyperdense to grey matter, with homogeneous enhancement following IV contrast injection. Less commonly the contrast enhancement was inhomogeneous, only one lesion failed to enhance. Disproportionately little oedema and mass effect compared with lesion size was noted on approximately half the CTs. Lesions usually touch either the ependymal lining of the ventricles or the leptomeningeal surface.