The aim of this study was to investigate and classify the internal morphology of the mesiobuccal root of upper first permanent molar, using the cone beam computed tomography. A total of 60 first permanent molars, not healthy and with intact pulp cavity, belonging to the Postgraduate dentistry bank, underwent the computed tomography. Axial images of each tooth were analyzed, and results showed that according to the number of conduits, 21 specimens (35%) had single conduit and 39 exhibited two conduits (65%). In reference to the types of internal configuration most commonly found according to Vertucci classification; type I (single channel that extends from the pulp chamber to the apex) was the most frequent (35%), followed by type II (two separate canals leaving the pulp chamber and joining next to the apex forming a single channel) with 30%. It was found that the morphology of the variation of mesiobuccal root, of upper first permanent molar is relatively high, and computed tomography proved to be an effective method for diagnosis.