Introduction: A case of unusual root morphology is presented to demonstrate anatomic variations in mandibular second molars. The most common configuration of mandibular second molars is to have two roots with three root canals; however mandibular molars may have many different combinations. Methods: Root canal endodontic treatment was performed in a mandibular second molar with three separate roots, two located distally and one mesially. Radiographically, all four root canals terminated with individual foramen. Results: Four orifices or four independent canals were found in three separate roots, indicating a rare anatomic configuration, and confirmed with the help of spiral computed tomography (SCT). Conclusion: Looking for additional roots, root canals and unusual morphology is an important part of successful root canal treatment, as the knowledge of their existence occasionally enables clinicians to treat a case that otherwise might have ended in endodontic failure. The use of SCT imaging in this case greatly contributed to a confirmed diagnosis and successful root canal treatment thereafter. Schlagwörter: radix entomolaris, spiral computed tomography scan, three-rooted mandibular second molar