Background/Aim: To analyze the internal morphology of mandibular incisors with two root canals using cone-beam computed tomography (CBCT). Material and Methods: 289 (143 central and 146 lateral) extracted intact mandibular incisors were radiographed for detection of a second root canal. The teeth presenting a second root canal were imaged with CBCT and evaluated regarding: root canal type, the distance of the cementoenamel junction (CEJ) to the bifurcation of the canals and the distance of the canal fusion to the apical foramen (in teeth in which canals rejoined). Results: Out of 143 central and 146 lateral mandibular incisors, 41 (28.7%) and 44 (30.1%) teeth respectively showed a second root canal. Types II, III, V and an additional type to Vertucci’s classification were identified. Type III was the most prevalent and presented in 30 (73.2%) central and 34 (77.3%) lateral mandibular incisors with two root canals. The mean values of the distance of the CEJ to the canal bifurcation were 4.2 mm and 4.0 mm for central and lateral mandibular incisors respectively. The mean values of the distance of the canal fusion to the apical foramen 5.5 mm and 5.1 mm for central and lateral mandibular incisors respectively. Conclusions: Mandibular incisors with two root canals mainly present with Vertucci’s Type 3 canal configuration. The canal bifurcation was identified mostly at the coronal and middle thirds of the root, while the canal fusion occurred in the middle third of the root.