A 64-year-old man had transverse myelopathy that rapidly progressed without pain over the course of 1 day. The cerebrospinal fluid interleukin-6 (CSF IL-6) level was extremely high (1,120 pg/dl). Spinal cord magnetic resonance imaging (MRI) showed a longitudinal extensive lesion extending from Th8 to the conus medullaris. Despite treatment with steroids and cyclophosphamide, the symptoms worsened, and the range of sensory disturbance spread. MRI showed that the lesion expanded to Th3 over the course of 2 months. Neuro-Behçet disease (NBD) was diagnosed on basis of the high CSF IL-6 level and HLA-B51 positivity, and treatment with infliximab was begun. The sensory disturbance improved slightly, and the CSF IL-6 level fell to the normal range (7.0 pg/ml). It is important to include NBD, which rarely presents with extensive spinal cord lesion, in the differential diagnosis when patients present with acute transverse myelopathy without pain.