PURPOSE: The purpose of this study is to describe the findings of the transligamnetous type of the herniated lumbar disc (HLD) with magnetic resonance MR imaging. MATERIALS AND METHODS: We retrospectively analyzed the MR images of surgically proven 20 cases of transligamentous type of HLD from January 1, 1992 to August 20, 1992. The MR imaging was performed with 1. 0T MR unit, using sagittal spin echo (SE) and axial gradient echo (GE) techniques. RESULTS: The results were as follows;1) the interruption of black line of the posterior longitudinal ligament (PLL) was identified in 19 levels and 17 levels in sagittal SE and axial GE images, retrospectively;2) the widening of adjacent epidural fat space was demonstrated in 16 cases of central or posterolateral HLD. The herniated disc material, as compared with the parent intervertebral disc, showed intermediate signal intensity (SI) in 19 and low SI in 1 level on T1WI, high SI in 10, intermediate SI in 7, low SI in levels on T2WI, and high SI in 10, intermediate SI in 9, low SI in 1 level on GE images. CONCLUSION: The most important sign of the transligamentous type HLD on MRI was the interruption of the black line with additional finding of the widening of adjacent epidural fat space. The MR signal intensity of the herniated disc was variable. Axial GE image was valuable for the evaluation of the direction of HLD and it relationship with neural structure, but had no addiational information for the degree and biochemical change of HLD over SE image.