An accurate diagnosis of the morphology of the root canal system is a prerequisite for successful root canal treatment. A review of the literature reveals a low incidence of three root canals. Diagnostic means, such as pre-operative radiographs and examination of the pulp chamber floor, are helpful in locating root canal entrances. This case report describes the successful treatment of maxillary second premolars with three root canals. Parole chiave: anatomical variation, maxillary premolar, root canal anatomy