PURPOSE: To evaluate the MR findings of neuro-Behcet's disease, and changes occurring during follow up. MATERIALS AND METHODS: Brain MR imaging was performed in 19 patients in whom neuro-Behcet's disease had been clinically diagnosed. After treatment with corticosteroids and immunosuppressive agents, 23 follow-up MR images were obtained in 12 patients, and a total of 42 MR images were retrospectively reviewed by two radiologists. RESULTS: Of the 19 patients, 17 (89%) had parenchymal lesions, and the other two had dural venous sinus thrombosis. Among the 17 patients with parenchymal lesions, three showed leptomeningeal enhancement. A total of 72 parenchymal lesions were detected on initial MR images; 55 (76%) were patchy or nodular in shape and the lesion of the internal capsule appeared linear. Seventeen lesions (24%) in 12 patients were confluent. In order of frequency, the involved sites were the pons, midbrain, thalamus, basal ganglia, internal capsule, and frontal lobe. Thirteen lesions of 39 lesions detected on postcontrast images were enhanced, and a mass effect was seen in the area of 16 parenchymal lesions. Associated findings were microhemorrhage of the brain in two patients and spinal cord involvement in one. On short-term follow-up images obtained 1 week to 2 months after intensive treatment during the acute stage of the illness, the leptomeningeal enhancement seen in three patients had decreased and most parenchymal lesions showed improvement. Long-term follow-up images obtained 3 months to 3 years later showed that parenchymal lesions had relapsed in five patients, and brainstem atrophy had developed or progressed in five others. CONCLUSION: The most characteristic MR finding of neuro-Behcet 's disease is multiple non-hemorrhagic lesions involving the brainstem. Leptomeningeal enhancement and dural venous sinus thrombosis may also be noted. On follow-up MR, the lesions may show either improvement or aggravation, and brainstem atrophy is not uncommon.