To evaluate the evolution of apical formation on 28 necrotic immature permanent teeth treated with calcium hydroxide at different stages of root development.Apical formation in 28 necrotic incisors was carried out (27 upper and one lower incisors), in children between the ages of 6 and 13 years old (11 males, 10 females). Following anesthesia and rubber dam isolation, the chamber was opened and the coronal and root pulp tissue was removed. Next, after measuring the canal, the root canal was irrigated with 5% sodium hypochlorite. Once the canal was dried, it was filled with the CaOH2 powder mixed with physiologic saline solution to a dense consistency but malleable. This paste was compressed into the canal using a cotton pellet. The canal was completely filled up to the apex. Finally, the cavity opening was sealed with zinc oxide-eugenol (IRM) and glass-ionomer (Vitrebond). Follow-up appointments were made every 3 months in order to evaluate the evolution of the periapical radiolucency and the formation of the apical barrier.The duration of the apical induction was 8.6 +/- 5.36 months. Increase or lack of growth in the length of the root canal and the type of root end closing was as follows: cementoid tissue (85.72%); osseous tissue (14.28%), with a 100% overall success rate. The evolution of these teeth was monitored over a 2-year period with re-infections occurring in 7.1 percent of the cases.