A retrospective study of 624 lumbar myelographic and CT myelographic procedures was undertaken to evaluate the frequency, radiographic and clinical relevance of contrast medium outside the dural sac. Our findings indicate that epidural contrast is frequently identified on CT scans with highly sensitive window settings (in 35.4% of all CT myelographic studies). Standard myelographic films are less sensitive for the detection of epidural contrast (9.6%). Subdural contrast is far less often encountered (in 2.4% of CT myelographic studies and in 3.2% of standard myelographic films). We believe leakage of contrast to occur through the puncture site into the epidural and subdural space.