Radiographs of 22 normal patients and 35 patients with proven epidural disease were correlated with CT scans to determine the range of normal and abnormal appearances of the osseous surfaces marginating the spinal canal. A subtle but useful plain film clue to early epidural disease was indistinctness of the posterior vertebral body margin, which in at least one case was the solitary radiographic sign of epidural metastasis. The radiographic distinctness of each of the bony margins of the spinal canal varied predictably with spinal level in normal individuals owing to systematic variations in obliquity. Indistinctness of an osseous spinal canal margin, interpreted with knowledge of the range of normal anatomy at the appropriate level, may provide the earliest plain film clue to the presence of spinal epidural disease.