Abstract Background context: Thoracic disc herniation is a rare condition. Distinguishing between a herniated disc and tumor for a lesion found at the thoracic level can be a diagnostic challenge. Purpose: To describe a case of thoracic disc herniation that mimicked a spinal cord tumor. Study design/setting: Case report and review of the literature. Patient sample: Case report. Outcome measures: Report of postoperative symptoms. Methods/description: A 54-year-old man was admitted to the hospital with progressively worsening weakness in both lower extremities, increased numbness of both lower extremities, pain radiating into his groin bilaterally and left foot drop. During a recent visit to his family physician, the patient's legs gave out and he collapsed. Physical examination revealed markedly increased tone in both extremities. Magnetic resonance images at T11–12 showed signal abnormality in the anterior extradural space, which extended posterior and inferior to the disc level to the left of midline. An extramedullary lesion found in the posterior spinal canal showed a low signal on T1 image and a high but heterogeneous signal on T2-weighted images. Preoperative diagnosis was neoplasm. A bilateral decompressive laminectomy was performed under operative magnification and ultrasonography. A large extruded disc was found that migrated from the ventral aspect around the thecal sac and into the dorsal aspect, which compressed the sac to the right. The extradural lesion was dissected off the surrounding thecal sac. Postoperatively, the patient underwent rehabilitation and is able to walk with only minimal weakness of both legs. Conclusions: Determining the diagnosis for thoracic spinal lesions, either disc herniation or tumor, is a diagnostic challenge.