SummaryAn autopsy case of chronic disseminated encephalomyelitis has been examined. The relevant history extended over a period of six years, and was characterized by recurrent exacerbations and remissions, primarily of the brain stem symptoms. The clinical picture resembled that of multiple sclerosis, but was accompanied by Behqet's syndrome during the later course of the illness. The differential diagnosis of this case has been discussed with special reference to the demyelinating diseases and the central nervous system complications of Behqet's syndrome.A man of 26 years of age experienced onset of his illness with intermittent twitchings of both legs, and four years later he developed double vision, dysarthria, nystagmus, blurred vision, constipation, urinary retention, and disturbed gait. Mentally, he was euphoric with occasional pathological laughing and weeping. These symptoms and signs fluctuated frequently and were accompanied by intermittent high fever of unknown origin, purulent erythematous papules, and both labial and scrotal ulcers. Terminally, he became dyspneic and expired in a comatose state.Neuropathologically, the main lesions were confined to the brain stem, but were also widespread from the diencephalon to the spinal cord, and to the optic nerve. They corresponded well with the clinical picture mentioned above. Histologically there were poorly defined perivascular foci of demyelination, especially those in the white matter being confluentially disseminated. Perivenous spaces in the lesions were remarkably dilated and laden with numerous fat granule cells, and glial fibers proliferated in varying degrees. Except for certain circumscribed areas, inflammatory cell infiltrations in demyelinated foci of long‐standing were absent. Both nerve cells and neuroaxons in the foci, on the other hand, were comparatively well‐preserved. In the severely damaged ireas swelling and fragmentation of the axons were observed. In the spinal cord, the lateral pyramidal tracts showed a marked secondary degeneration bilaterally with corresponding gliosis. In Goll's tracts, symmetrical demyelination was found, which might indicate a systemic degenerative process.The above‐mentioned pathoanatomical findings suggest that the present case may belong to the category of demyelinating encephalomyelitides in a broad sense. The central nervous system involvement in the fatal cases of Behset's syndrome have not often been reported in the literature. To the best of our knowledge the present case demonstrates some unusual clinico‐pathological f