OBJECTIVE: To observe the contrast spreading patterns in the retrodiscal (RD) approach for transforaminal epidural steroid injections and their effect on pain reduction. METHOD: Patients with L5 radiculopathy who were scheduled to receive lumbar TF-EPB were consecutively included. We randomly divided them into the L4-5 RD and L5-S1 RD groups and administered 1 cc of contrast dye into epidural space. We observed the shape and the location of contrast dye on the anterior-posterior and lateral views. We injected 1 cc of 0.5% lidocaine mixed with 20 mg of triamcinolone, and checked the pain intensity before and two weeks after the procedure by using visual analogue scale (VAS). RESULTS: In the L4-5 RD group (n=30), contrast spread over the L4 nerve root in 27 cases and the L4 and L5 nerve roots in 3 cases. In the L5-S1 RD group (n=33), contrast spread over the L5 nerve root in 20 cases, the S1 nerve root in 3 cases, and the L5 and the S1 nerve roots in 10 cases. The contrast spreading patterns could be divided into 4 patterns: the proximal root in 40 cases, the distal root in 19 cases, the anterior epidural space in 3 cases and an undefined pattern in 1 case. CONCLUSION: In RD lumbar TF-EPB, the contrast dye mostly went into the cephalic root and about 60% spread over the proximal nerve root. There was less pain reduction when the contrast dye spread over the distal nerve root.