The C-shaped canal system is an anatomical variation mostly seen in mandibular second molars, although it can also occur in maxillary and other mandibular molars. Such variation in the root canal anatomy is uncommon in mandibular first premolars and very rare in mandibular second premolars. The C-shaped canal is so named for the cross-sectional morphology of the root and root canal. The main anatomic feature of C-shaped canals is the presence of a fin or web connecting the individual root canals. Failure of the Hertwig's epithelial root sheath to fuse on the lingual or buccal root surface is the main cause of C-shaped roots, which always contain a C-shaped canal. This case report describes an unusual occurrence of C-shaped roots in mandibular first and second premolars bilaterally, diagnosed with the aid of spiral computed tomography. Key words:Canal configuration, C-shape, mandibular first premolar, mandibular second premolar, spiral computed tomography scans.