Aim: This study presents the results of a retrospective evaluation of treatment of immature non-vital teeth using mineral trioxide aggregate (MTA) for root-end closure. Methods: Forty-six teeth with incomplete root development presenting with apical periodontitis were treated at a dental office limited to endodontics using MTA for apical closure. Success of treatment was defined as absence of clinical symptoms or radiographical signs of pathology and was assessed at least 1 year after treatment. The radiographs were evaluated by two calibrated endodontists. Results: Follow-up examination was performed on 95.6% (n = 44) of the teeth included in the study. The mean recall interval was 2.6 years. Success rate for the evaluated cases was 72.7%. Conclusion: This study showed a significant correlation between the success rate and the length of the recall interval (t-test, P = 0.046). The success rate significantly increased with increasing recall intervals. Keywords: apical barrier, apical closure, clinical outcome, immature apices, MTA, open apex, recall interval