Intravascular lymphomatosis (IVL), a rare type of non-Hodgkin's lymphoma, is an uncommon cause of progressive dementia, usually followed by death within a few months of onset of clinical disease. Often this aggressive tumor is only diagnosed at autopsy, because of misleading clinical features mimicking a broad spectrum of syndromes and the absence of circulating lympoma cells in the blood, bone marrow or cerebrospinal fluid in many cases. Here we present IVL in a 78-year-old woman with findings leading to the clinical diagnosis of vascular dementia with sudden beginning and positive 14-3-3 protein in the CSF, commonly reported in Creutzfeldt-Jakob disease (CJD).