The case of a 50 year old man with personality changes, dementia, and brain stem symptoms is presented. Magnetic resonance imaging (MRI) disclosed high signal areas mainly in the brain stem. Both a positive skin prick test and an HLA-B51 were demonstrated. These clinical findings were suggestive of neuro-Behçet syndrome, although there were no mucocutaneo-ocular symptoms characteristically associated with this disease. The relationship between neuro-Behçet syndrome and brain stem encephalitis, including a discrimination from multiple sclerosis, is discussed.