Although the most common configuration for mandibular first molars is two roots and three root canals, there are potentially many different combinations. A case of unusual root canal morphology is presented in this report to demonstrate anatomical variations in mandibular molars. Root canal treatment was performed in a mandibular first molar with three separate roots. Examination of the pulp chamber floor revealed four separate canal orifices. However, the working length radiograph showed that the four root canals ended in three distinct foramen (two of the mesial canals were confluent). Cases of three orifices or three independent root canals in the mesial root are not uncommon, but there are very few cases of a first mandibular molar with three separate and divergent roots, which is a rare anatomical configuration. The present report is a reminder of the importance of looking for additional canals and unusual canal morphology, because knowledge of their existence will enable clinicians to treat a case successfully. Schlagwörter: anatomical variation, endodontic treatment, mandibular molar