Objective: This retrospective study aimed to collect information about the long-term outcome of apexification treatment with mineral trioxide aggregate (MTA) of teeth with open apices. Method and Materials: A total of 98 teeth in 79 patients (m:f = 1:1.3) who had completed endodontic apexification treatment with MTA between September 2005 and January 2014 at a university dental clinic were considered. Both initial treatments and retreatments of former root canal treatments other than apexification were included. All patients were invited for a standardized follow-up visit. Data regarding age, sex, tooth type, reason for treatment, detailed treatment protocol, clinical and radiographic findings, treatment quality, and outcome were also collected from the patients' records. Descriptive statistical analysis was performed. Results: In the majority of cases, endodontic treatment was related to trauma with fracture (45/98, 45.9%) and luxation injuries (20/98; 20.4%), followed by unknown causes (12/98; 12.2%), retreatments (7/98; 7.1%), hypophosphatasia (7/98; 7.1%), and caries (1/98; 1%). In the beginning, the Periapical Index (PAI) showed pathologic findings with a PAI > 2 in approximately 50% of cases, while 25% presented with minor or an absence of findings. At the end of the observation period, more than 90% showed clinical-radiographic success, whereas eight teeth were associated with an elevated PAI. Only 5% of cases needed further dental treatment, such as root-end surgery or retreatment of the root canal treatment. Conclusion: Within the limits of this retrospective investigation, clinical and clinical-radiographic success of the apexification treatment appears to make this a good and reliable treatment option for teeth with open apices. Keywords: apexification, apical barrier technique, dental trauma, endodontic treatment, mineral trioxide aggregate, open apex