In patients with intravascular lymphomatosis (IL) a broad spectrum of neuro-psychiatric disorders including dementia, focal neurological signs and seizures has been reported. Clinical diagnosis is difficult since neuroimaging findings are nonspecific. The clinical histories, biopsy and autopsy findings of three patients with IL, one with brain biopsy, are described. Two of them presented with rapidly progressive, fluctuating dementia. The third patient suffered from seizures followed by aphasia. Histology revealed large-cell lymphoma of the B cell type. The prognosis of IL, in general, is poor.