Intravascular lymphomatosis is a rare variant of non-Hodgkin's lymphoma with an unusual predilection for the central nervous system. Most cases are not diagnosed until postmortem because of variable clinical presentation and non-specific laboratory findings. We studied a 41-year-old lady who presented with progressive neurological symptoms. MR showed multifocal grey and white matter lesions. Brain biopsy showed an intravascular lymphoma of the B-cell lineage. This report illustrates the ischaemic origin of the radiological lesions, as they are all hyperintense on the diffusion-weighted images. This has, to our knowledge, never been published before. MR did not show any enhancement after intravenous Gadolinium-DTPA (parenchymal or meningeal)which is a very uncommon finding in this entity. Intravascular lymphomatosis should be taken into account in the differential diagnosis of repeated cerebral ischemia of unclear aetiology.