Aim: The purpose of this study was to emphasise the importance of familiarisation with the internal anatomy of the mesial root of human permanent mandibular molars. Materials and methods: A literature review was conducted and four clinical cases of mandibular molars exhibiting an additional middle mesial canal are presented. Non-surgical treatment and retreatment procedures are described. Results: The middle mesial canals in all cases demonstrated a merging configuration with either the mesiobuccal or the mesiolingual canal. Acknowledgement of this configuration bears significant clinical implications. Enhanced magnification and illumination were indispensable for the detection and negotiation of the intermediate canal. Conclusions: The middle mesial canal constitutes an anatomic component that needs to be acknowledged during endodontic treatment of the mandibular molars. Awareness of its occurrence along with visual augmentation may aid a higher detection rate. Schlagwörter: mandibular molars, middle mesial canal, root canal anatomy