Nine cases of neuro-Behcet's disease were investigated clinicopathologically. Pathological pictures of the central nervous system were characterized as follows: the site of predilection was the brain stem, followed by the spinal cord, cerebrum and cerebellum. The pathognomonic changes were recurrent inflammations around small vessels, causing a softening of the tissue. Lesions were composed of a perivascular infiltration of lymphocytes, histiocytes and microglias and, moreover, diapedesis, degenerated nerve cells and oligodendroglias, glial nodule, breakdown of myelin and axon, fatty granule cells and glio-mesenchymal proliferation were present occasionally. Electron microscopic studies on the neurons revealed no evidence of viral particles except for some accumulations of electron dense bodies.