This case report deals with the endodontic management of a mandibular second premolar with a category 3 C-shaped root canal configuration, aided with cone beam computed tomography (CBCT) for the proper diagnosis and clinical management planning of the case. It also discusses use of a rotary file system such as XP-Endo that respects the root canal anatomy and the possible role of calcium hydroxide in the healing of a large apical lesion - all of this proven by periodic evaluations with radiographs and post-treatment CBCT. Schlagwörter: C-shaped root, C-shaped root canal, cone beam computed tomography, dental anomalies, mandibular premolar root canal