Magnetic resonance imaging (MRI) examinations of 23 patients with neuro-Behçet's disease were evaluated to correlate the results with clinical, X-ray CT, and positron emission tomography (PET) findings. The results were as follows: Focal lesions were detected in 17 (73.9%) and brain atrophy was depicted in 10 (43.4%) out of the 23 patients. This ratio was higher than X-ray CT. The acute phase lesions detected by MRI at the first medical examination were diminished after the treatment in proportion to the improvement of the clinical symptoms. Cerebral blood flow study and glucose metabolism study by PET were performed on patients whose main problems were mental symptoms. Both cerebral blood flow and glucose metabolism were decreased in these patients. These results suggest that MRI is a useful technique for detecting the central nervous system lesions of neuro-Behçet's disease and monitoring its clinical status and therapeutic response for this disease, and PET provides a useful way of understanding the haemocirculatory and metabolic aspects of this disease.