There are few reports on treatment of necrotic pulps with mineral trioxide aggregate (MTA) for apexification. Five immature teeth with necrotic pulps were treated with the use of an apical plug of MTA for apexification. All teeth were central incisors that had premature interruption of root development caused by a previous trauma. According to the treatment protocol, the root canals were rinsed with 5% NaOCl; then calcium hydroxide paste was placed in the canals for 1-6 weeks. The apical portion of the canals were filled with MTA. The rest of the canals were obturated with lateral condensation of the gutta-percha applied with a canal sealer. At 6 months, 1 year and 2 year follow-up periods the clinical and radiographic appearance of the teeth showed the resolution of the periapical lesions and continued root end development in all except in the one case in which the MTA was extruded out the apex. MTA can be considered a very effective option for apexification with the advantage of reduced treatment time, good sealing ability and high biocompatibility.