Objective: The aim of the study was to detect the prevalence of middle mesial canals in the mesial root of first mandibular molars in Egyptian population by retrospective analysis of a large number of cone-beam computed tomography (CBCT) scans. Materials and Methods: A total of 1090 CBCT scans of first permanent mandibular molars were obtained from patients who visited the Faculty of Dentistry, Cairo University, Egypt, for various purposes. CBCT scans were searched and only 800 subjects (374 males and 426 females) fulfilled the inclusion criteria. Results: Middle mesial canal was present in 25.6% (205 of 800) of the subjects. The incidence of middle mesial canal bilaterally was 5.9% and unilaterally was 19.8%. There was no statistically significant difference between males and females (P=0.079). Regarding the distribution of canal (Bilateral and unilateral); there was also no statistically significant difference between males and females ( P =0.056). Conclusion: Among mandibular first molars, there is a high prevalence of a middle mesial canal in the Egyptian population. Detection of its presence is essential to achieve successful endodontic treatment.