In order to define the patterns of neurological involvement in Behcet's disease and to assess prognostic factors, 558 files of the neuro-Behcet out-patient clinic were reviewed. Those patients without any evidence of objective neurological involvement as well as the patients with other possible explanations for the neurological picture, and cases not fulfilling the criteria for Behcet's disease were excluded. The remaining 200 cases (155 male, 45 female) were evaluated: 162 had parenchymal CNS involvement (brainstem or 'brainstem +' involvement in 51 %, spinal cord involvement in 14%, hemispheric involvement in 15% and isolated pyramidal signs in 19%) while 38 had secondary or non-parenchymal CNS involvement. In the first group the most common findings were pyramidal signs, hemiparesis, behavioural changes and sphincter disturbance, whereas in the second group the syndrome of raised intracranial pressure due to dural sinus thrombosis was the main clinical manifestation. In 60% of the cases with parenchymal involvement, CSF was hypercellular and/or had an elevated protein level, whereas in cases with non-parenchymal involvement the CSF was usually normal except for the elevated pressure. In more than half of the patients with parenchymal involvement, MRI showed brainstem and/or basal ganglion lesions. Forty-one per cent of the cases had a course with at least one attack and remission, another 28% also had attack(s) but showed secondary progression, 10% had primary progression and 21 % had silent neurological involvement. Survival analysis was performed in patients who had at least a 3-year duration of neurological disease. Parenchymal involvement, elevated protein and/or pleocytosis in the CSF,'brainstem +' type involvement, primary or secondary progressive course and relapse during steroid tapering were all associated with a poorer prognosis.