Treatment of nonvital immature permanent teeth with calcium-hydroxide is associated with some difficulties such as weakened tooth fracture, root canal reinfection and long treatment time. Mineral trioxide aggregate (MTA) apical plug method is an alternative treatment option for open apices, and has gained popularity in the recent times. In this case report, we have attempted to present successful treatment of three maxillary incisors with open apices and periapical lesions with MTA. After preparing the access cavity, the working length was determined. The root canals were irrigated with 2.5% Sodium hypochlorite (NaOCl) and disinfected with calcium-hydroxide for two weeks. MTA was then placed in the apical 3 millimeters of the root canal. The remaining part of the root canal was filled with gutta-percha and the coronal restoration was finished with composite resin. After six months the radiographic examination showed a decrease of periapical lesions. At a 1-year and 18-months follow up, radiological and clinical successful healing of the incisor teeth was seen. MTA seems as an effective material for the apical plug method for the treatment of nonvital immature permanent teeth with open apices.