Dorsal epidural migration of an extruded disc fragment is an infrequent event, especially in the thoracic spine. An uncommon case involving a 55-year-old man is presented, with a 1-month history of paraparesis and thoracolumbar pain. Magnetic resonance imaging demonstrated a dorsally located, extramedullary mass at the T10-T11 intervertebral level. The lesion was suspected to be a tumor. The patient underwent a T10-T11 laminectomy. Intraoperatively, an encapsulated mass of soft tissue adherent to the dural sac was found. The pathologic diagnosis was inflammatory tissue and disc material. Six months after the operation, the patient remained asymptomatic, and radiologic control showed no residual mass. Although rare, a sequestered disc fragment should be included in the differential diagnosis of an enhancing posterior extramedullary thoracic mass. Preoperative diagnosis of such pathology is difficult because the clinical signs and radiologic images may not entirely exclude other more common thoracic spinal lesions, especially tumors.