A 60-year-old woman complained of low back pain radiating to both buttocks and to the anterior aspect of the left thigh. MRI showed a left posterolateral epidural mass at the L1-L2 level. An epidural abscess was suspected, but the biochemistry was normal. Excision yielded complete relief of symptoms. Pathological examination demonstrated that the specimen was a migrated disc fragment. The authors found 29 other cases of disc migration to the posterior epidural space; two of these were at the thoracic level. Eleven of the 27 lumbar cases (40%) were complicated with Cauda Equina Syndrome (CES). MRI is the method of choice to make the diagnosis. The differential diagnosis includes tumour, haematoma and abscess.