Aim: The objective of this case report is to present a successful root canal treatment of a maxillary first molar having three mesiobuccal canals with separate orifices. Case presentation: An 18 year old female patient was admitted to our clinic, complaining from severe pain. We observed during the clinical examination that root canal treatment of the maxillary right first molar was already initiated. The tooth was percussion sensitive, cold and heat sensitive, although there was no referred pain. A broken endodontic instrument in the disto-buccal root canal was found during the radiographic examination. After extensive clinical and radiographic examination tooth was prepared for nonsurgical endodontic treatment. Starting the endodontic treatment, it was observed the presence of two canals orifices in the buccomesial root with no preparation. Though we failed to remove the fracture for the endodontic instrument, the instrument was bypassed. Root canals were obturated with guttapercha and sealer. The tooth was restored with composite resin. Conclusion: Recall examination as far as 6 months post-treatment found no sensitivity to percussion or palpation and recall radiography after treatment show no evidence of any periradicular lesion.