Deviations from the norm in root canal morphology are not uncommon. Dental clinicians should keep this possibility in mind whenever they perform root canal treatment. The root canal treatment of a mandibular molar with aberrant canal configuration can be diagnostically and technically challenging. The astute clinician must be aware of recent literature that states that the mandibular first molar has a 1-15% chance of a fifth canal. This poster reveals clinical management of a mandibular first molar with multiple mesial canals and also demonstrates a clinical case that contained a fifth canal i.e. the middle mesial canal. A good knowledge of possible variations in root canal morphology and a little extra effort to search for additional canals can go a long way in improving the long-term prognosis of the tooth in question. Palabras clave: mandibular first molar, multiple mesial canals, middle mesial canal, root canal morphology