Clinical case: Male patient, caucasian, 53 years, referred by its general dentist, because he could not find the canals. The tooth presented an initiated endodontic therapy and it was diagnosed with symptomatic apical periodontitis. The treatment plan consisted in endodontic therapy, with a good prognosis, followed by the realization of a post and crown, due to the big coronal destruction. The T-shaped modified access cavity was done, to identify the 2 vestibular canals and the palatal one. The working length has been determined with an electronic apex locator and the instrumentation has been done with ProtaperNext system. It has been done a copious irrigation with 5% sodium hypochlorite and the obturation has been done with thermoplastic techniques. Discussion: The incidence of 3 canals in maxillary premolars is low (0.5 - 6%), varying in the second premolar between 0.3 and 2%. It occurs mainly in caucasian population and it's almost nonexistant in asian population. It's necessary to do preoperative radiographs both centred and angulated, in order to detect the internal anatomy, as well as the number of roots. The use of cone beam computerized tomography is advised in the detection of a less usual anatomy. Conclusions: Through the correct access cavity in this type of anatomy, as well as the use of the operating microscope, the 3 canals were identified and treated. A good planification, associated with anatomical knowledge, a good diagnosis, and the use of magnification, allow the success of this type of treatments. Keywords: maxillary premolar, 3 canals