A case of neuro-Behçet's disease manifested as chronic progressive cerebellar ataxia is reported. A 56-year-old woman had suffered from recurrent oral aphthous ulcers, genital ulcers and polyarthritis since her late twenties. At age 53, she noticed small stepped-gait; at age 55, she developed scanning speech, a wide-based gait and memory disturbance. On admission she had oral aphthous ulcers, scarring of genital ulcers and polyarthralgia. A neurological examination revealed memory disturbance, saccadic eye movement, scanning speech, a slow tongue wiggle, moderate limb and truncal ataxia and moderate hyperreflexia in four limbs without pathological reflexes. Relevant laboratory examination data showed a positive HLA-B51. The cerebrospinal fluid (CSF) had a mild elevation of the cell counts and the amounts of protein. Brain magnetic resonance imaging showed mild atrophy of the cerebellum and brainstem. Fluoro-2-deoxyglucose-positron emission tomography showed a decreased glucose metabolism in the cerebellum and brainstem. Methylprednisolone pulse therapy (1 g x 3 days) followed by oral corticosteroids (50 mg/day) with gradual tapering markedly alleviated the cerebellar ataxia. The presence of oral and genital ulcers and CSF pleocytosis as well as effectiveness of corticosteroids in relieving the neurologic symptoms suggested neuro-Behçet's disease. We propose the existence of a new subtype of neuro-Behçet's disease characterized by chronic progressive cerebellar involvement possibly due to microvasculitis for which corticosteroids may be effective.