It is essential to locate and treat extra roots, such as radix entomolaris and paramolaris, when performing root canal treatment. This study aimed to determine the prevalence and morphology of extra-roots in mandibular molars of a Chilean subpopulation. 1000 Cone-beam computed tomography (CBCT) scans were included, obtaining a sample of 3260 first, second and third molars. Each molar was analyzed to determine the presence of an extra root. Extra roots were further analyzed to measure length, angle of curvature, and classification by De Moor. First molars presented a prevalence of extra roots of 3.31 %, second molars of 2.63 %, and third molars of 4.71 %. Considering the type of radix, 2.2 % of the total sample presented radix entomolaris, 0.79 % radix paramolaris, and 0.24 % both types of radix. The most common configuration for radix entomolaris was type 3 of the De Moor classification, and for radix paramolaris was type 1. In a Chilean subpopulation, 3.3 % of the mandibular molars presented radix entomolaris, paramolaris, or both. Regarding morphology, radix entomolaris showed severe curvatures. No significant associations were found regarding gender and extra-roots.