In 220 patients in whom ventral fusion according to Cloward was performed because of traumatic or degenerative discopathy, the pre-surgery finding of discography was compared with the finding established during the operation. It was found that pre-operative discography enables to diagnose damage of the nucleus pulposus and anulus fibrosus, as well as tearing of the posterior and anterior longitudinal ligament. It is emphasized that in degenerative damage, escape of the contrast medium in ventral direction merely represents backflow of the contrast medium along the puncture channel and rarely represents rupture of the anterior longitudinal ligament. Side localisation is possible by means of the semioblique x-ray. In case of a traumatic damage, at least two disc spaces should be diagnosed.