Disk fragment relocation is commonly limited to the anterior epidural space, although posterior epidural movement of a sequestrated disk piece to the posterior epidural space is infrequent. We present an uncommon case of dorsal extradural sequestration of lumbar disk herniation. A 77-year-old man presented with severe leg pain, low back pain, and urinary incontinence. Deep tendon reflexes were inattentive at the knee and ankle, and the motor power in terms of ankle dorsiflexion and great toe dorsiflexion was 2/5 in both lower limbs. There was hypoesthesia in the S1, S2, and S3 dermatomes. Magnetic resonance imaging displayed a large isointensity lesion at the L4-L5 level on the T2 sagittal image, indenting circumferentially the thecal sac from lateral to posterior of the thecal sac. The patient underwent an L4-L5 central laminectomy. A large, solid epidural disk fragment was recognized dorsally, with major compression of the thecal sac. The patient report improved lower extremity motor function at three-month follow-up. A displaced disk fragment should be considered as causative when patients present with cauda equine syndrome and be treated as a surgical emergency.