To achieve successful endodontic treatment, the clinician should be aware of root canal anatomy and its variations. Finding mandibular premolars with three canals is rare and its prequency has been reported to be 0.46%. Undetected extra roots and canals are a major reason for failed root canal treatment. This report describes diagnosis and endodontic treatment of a mandibular second premolar with three canals, two orifices in buccal and one in lingual, and a mandibular first premolar with two orifices in lingual and one in buccal. Different studies report low prevalence of mandibular premolars with three canals, so careful evaluation by radiographic and clinical examinations, use of magnification devices, fiber optics and dyes is required for successful detection and access to extra root canals.