Brown-Sequard syndrome refers to a set of signs and symptoms caused by hemisection of the spinal cord from various sources. It may have multiple causes; traumatic injuries are the most frequent ones. The less common causes include inflammation, ischemia, tumors, or infections.This report is about a 12-year-old boy with an acute and progressive course of right hemisection of the spinal cord, with ipsilateral hypo/areflexic paralysis and contralateral loss of thermalgesic sensation. The MRI of the spinal cord showed inflammation in the right side of the spinal cord at the level of the second and third thoracic vertebrae. The patient was diagnosed with idiopathic transverse myelitis and was started on intravenous high-dose corticosteroids; he showed a favorable clinical course and recovered neurological functions.