A C-shaped root canal configuration is the most common anatomical variation of the root canal system and exists mostly in mandibular second molars, but may be found also in other teeth. The management of C-shaped canals is challenging for clinicians in diagnosis, shaping, cleaning and obturation because of the broad spectrum of canal configurations. This case report presents the diagnosis and treatment of a C-shaped canal in a mandibular first molar and discusses the use of CBCT in cases of unusual root canal anatomy. Keywords: calcium hydroxide, C-shaped canal, mandibular first molar