We present a case of Neuro-Behcet's disease with an unpredictable clinical course. A 47-year-old man was admitted to the neurosurgery department of our hospital with a mild headache. Three days after admission, his consciousness suddenly decreased and respiratory distress progressed rapidly. A brain MRI revealed that the previously observed abnormal signal had extended markedly to both the thalamic areas and the entire brain stem, and the surrounding brain parenchyma were compressed by cerebral edema. Based on the patient's symptoms of recurrent oral and genital ulcers, skin lesions, and uveitis, a rheumatologist made a diagnosis of Behcet's disease with CNS involvement. The patient was treated with high-dose methylprednisolone with respiratory assistance in the intensive care unit for 9 days and his neurologic symptoms improved remarkably. Neuro-Behcet's disease must be considered in the differential diagnosis in rapidly deteriorated young neurological patients along with a stroke, low-grade glioma, multiple sclerosis, and occlusive venous disease.