The root canal anatomy of a permanent mandibular first molar has been traditionally described as 2 roots--1 mesial and 1 distal--with 2 canals in the mesial root and 1 or 2 canals in the distal root. Nonetheless, other possibilities exist. The presence of a third canal in the mesial root has been reported to have an incidence of 0%-17%. Conventional radiographs are routinely used to determine root canal anatomy; however, these are 2-dimensional representations of a 3-dimensional object. Advanced diagnostic methods that can provide 3-dimensional data, such as spiral computed tomography (SCT), is very helpful in determining complex morphology. This case report presents the management of a mandibular first molar with 3 mesial and 2 distal canals, confirmed with the aid of both SCT and conventional radiographic methods.