Herniated nuclear material of the cervical disc often perforates the posterior longitudinal ligament. Of 22 patients who were operated on by an anterior approach, 10 were of this type (the subligamentous type of cervical disc protrusion), while in the remaining 12 patients and 15 discs the protruded disc caused no tear in the ligament (the epiligamentous type). Myelography and CT myelography of these patients were reviewed. On CT myelography a localized and sharply demarcated excavation of the metrizamide ring was commonly found in the subligamentous type. Myelographic lateral view in this group shows a moderate or large indentation of the metrizamide column, since the herniated nucleus pulposus sometimes migrates caudally or cephalically. A small myelographic deformity coupled with diffuse excavation of the metrizamide ring on a CT myelogram leads us to the diagnosis of the epiligamentous type of cervical disc protrusion. In such cases, excision of the ligament is unnecessary during exploration of the discs, except when there is marked depression in the posterior longitudinal ligament. Presurgical recognition of both anatomical processes must be stressed for anterior discectomy.