Lumbosacral radiculopathy is a challenging diagnosis, and Electrodiagnostic study (EDX) is a good complementary test for Magnetic Resonance Imaging (MRI). Physical examination, MRI and electrodiagnosis have different diagnostic values in this regard. MRI can provide anatomical evidence and is useful in choosing a treatment process, but it could also have false positive results. In this study, we assessed the correlation of clinical and electrodiagnostic findings in patients with positive MRI findings for S1 radiculopathy. EDX was performed for 87 patients referred with clinical and MRI diagnosis of S1 radiculopathy. The consistency between EDX results, MRI, and clinical findings were evaluated by Pearson chi 2 and odds ratio. Fifty-eight percent of patients had disc protrusion, and 42% had extrusion. Physical examination revealed absent Achilles reflex in 83% and decreased S1 dermatome sensation in 65%. In this study, EDX sensitivity was about 92%. The highest consistency among EDX parameters and physical examination findings was between absent Hreflex and decreased Achilles reflex (OR=6. 20, P=0. 014), but there was no significant consistency between Hreflex and neither muscular weakness nor SLR test result (P>0. 05). There was also no relationship between type of disc herniation in MRI and H reflex. There was correlation between H-REFLEX abnormalities and absent ankle reflex in patients with unilateral L5-S1 disc herniation in MRI. Results of this study showed that in patients with positive MRI for L5-S1 disc protrusion and S1 nerve root compression, it is still beneficial to perform EDX for selected patients.