This case report deals with the endodontic treatment of a relatively uncommon clinical case, i.e., the treatment of three canals with three separate foramina in both the first and the second mandibular premolars in the same patient. It is further concluded that for such a treatment to be successful, an accurate diagnosis of the morphology of the root canal system should first be reached and, accordingly, some resources such as radiographs, cone beam computed tomography (CBCT) as well as the operating microscope should necessarily be made use of. Schlagwörter: cone beam computed tomography, mandibular first premolars, mandibular second premolars, operating microscope, three canals, three foramina