Introduction: The knowledge of root canal anatomy is essential to ensure a successful outcome of surgical and nonsurgical root canal treatment. The aims of this article were to present 2 cases of maxillary molars with 3 mesiobuccal root canals and to review the available literature on this anatomic variation. Methods: The first case described a nonsurgical root canal treatment of tooth #16 in a 29-year-old man with the aid of a dental operating microscope. In the second case, an extracted maxillary right first molar was scanned by a micro- computed tomographic system and reconstructed 3- dimensionally using modeling software. Results: In both cases, the mesiobuccal root had 3 canals (type 3- 2 in case I and type 3-3 in case II), whereas the distobuccal and palatal roots had a single canal. The literature review showed that the overall incidence of 3-canaled mesiobuccal roots in maxillary molars ranged from 1.3%-2.4% and that the most common root canal configuration was type 3-2. Conclusions: Clinicians should always anticipate the presence of extra canals in maxillary molars and use all the available tools to locate and treat these. Copyright © 2014 American Association of Endodontists.