Human mandibular canines do not present an internal anatomy as simple as could be expected; there are canines with a single root and two canals, two roots or fused roots. The existence of mandibular canines with more than one root canal is a fact that clinicians ought to keep in mind, in order to avoid failure during endodontic treatment. In spite of the low incidence of canines with one root and two canals or two roots, this possibility cannot be forgotten. These morphological variations raise difficulties in endodontic treatment.This article presents two clinical cases of mandibular canines with two canals in the same root and with two roots and two canals. In both cases the canines were used as abutments for a prosthetic restoration and both went undetected on the usual X-rays examination. In the first case the second canal was found during the endodontic treatment steps and its presence was confirmed with a second X-ray from another incidence. The second case is a retreatment followed by a surgical phase. The precise knowledge of the endocanalicular system's anatomy is essential for the success of the root canal therapy. The failure to detect all the canals and the incomplete canal filling ultimately results in the loss of the tooth. The long term success of the prosthodontic treatment depends directly on the quality of the endodontic treatment of the abutments. The mandibular canine is very important for any type of prosthetic restoration. The clinical cases reported show that such anatomical variations can also occur in Romanian population as much as described in the international literature and cannot be overlooked in private practice. Keywords: anatomical variation, mandibular canine, endodontic treatment