Objective: To estimate the prevalence of radix entomolaris (RE) in the permanent mandibular first molars in Saudi Sub-population. Materials & Methods: A total of 2154 radiographs were selected and interpreted by two independent interns for the presence of extra root (RE). 154 radiographs were excluded and 2000 peri-apical radiographs were selected to represent the study sample. Data were analyzed and the prevalence of the RE was then calculated. Results: Only 144 cases were diagnosis with an RE. The prevalence of RE among Saudi subpopulation who visited the college of dentistry, King Khalid University was 7.2 %. This was evenly distributed in the right (74 cases) and left (70cases) sides, and between males and females with 76 & 68 cases, respectively. Conclusion: The prevalence of RE in Saudi subpopulation was 7.2 %, which is comparable to others except for mongoloid peoples. Initial diagnosis is essential to avoid ‘missed canals’ and improper treatment planning. Dental practitioners should be able to identify morphologic abnormalities in the permanent mandibular molars to achieve successful and satisfactory endodontic treatment outcome.