Intravascular lymphomatosis is characterized by the presence of large lymphoma cells predominantly within small vessels. This report presents two patients with diagnostically misleading neurological manifestation of this disease. Case 1, a 63-year-old man, developed a sensorimotor transverse spinal cord syndrome and encephalopathy. Lumbar puncture revealed albuminocytological dissociation. Magnetic resonance imaging (MRI) showed progression of multifocal infarct-like lesions in the brain, the thoracic cord and the medullary cone. Autoimmune inflammation was suspected, and the patient received immunosuppressive therapy with immunoglobulins, steroids and azathioprine. He died 18 months after the onset of symptoms. Case 2, a 68-year-old man, showed fluctuating aphasia, disorientation, and fever for several months. Brain MRI-scan, electroencephalography (EEG) and cerebrospinal fluid (CSF) cytology were inconclusive. Premortal biopsy of lesions in liver and right suprarenal gland showed no further characterized malignancy. He died 6 months after the first occurrence of symptoms. Autopsy of both cases revealed an intravascular lymphomatosis. Tumour cells were seen disseminated in extranodal sites including heart, lung, adrenal gland, spleen, thyroid gland and brain. An intravascular lymphomatosis should be considered when a meningoencephalitic symptomatology is unclear. A biopsy of different organs including the brain and leptomeninges should not be delayed to ensure ante mortem diagnosis and to initiate chemotherapy.