HNP [Herniation of the necleus pulposus] generally occurs at ventral portion of lumbar thecal sac due to the anatomical position. We report two unusual cases of herniated dorsal portion of lumbar thecal sac causing diagnostic difficulties. Two patients with posteriorly migrated epidural disc fragments were evaluated with plain X-ray, and magnetic resonance imaging. These patients responded well to operation with complete relief of symptoms. Definite diagnosis of posteriorly located disc fragments is difficult because the radiological images of disc fragments may mimic those of other more common posterior epidural lesions.