Study design: Case report. Objectives: To report an unusual case of Brown-Sequard syndrome (BSS) associated with idiopathic transverse myelitis (TM). Setting: Department of Neurosurgery, Chonnam National University Hospital, Gwangju, South Korea Methods: A 38-year-old man presented with left leg weakness and right-sided decrease in sensation at the T11 level below. Magnetic resonance images (MRI) of the thoracic spine showed diffuse swelling of the spinal cord spanning the fifth to the eighth thoracic vertebra. The lesion had high signal intensity on T2-weighted images. Eccentric nodular enhancement within the left anterolateral aspect of the spinal cord was appreciated with gadolinium administration. Results: The patient was treated with pulsed methylprednisone and showed marked improvement in neurological function within 3 days. An MRI at 5-month follow-up demonstrated complete resolution of the abnormalities. Conclusion: This case illustrates a rare case of BSS caused by idiopathic TM of the thoracic spinal cord. TM should be considered in the differential diagnosis of BSS.