Introduction: Root perforation is an endodontic procedural error. Treatmentof perforation depends on the location and size of perforation,duration of exposure to the oral cavity, patient's cooperation and degree oftissue inflammation. Several materials have been introduced to seal off the perforation. MTA is one of the best materials for this purpose.

  Case Report: We report the repair of distal root perforation in a primary mandibular second molar of a 9 year-old boy who had congenital absence of the second premolar tooth at the same quadrant. The perforation site was sealed with MTA and the three root canals were filled with gutta percha. Follow up visits at 1, 3, 6, 12, 21 and 24 months showed clinical and radiographic success of treatment.