The normal development and maturation of a root depends on a vital, healthy pulp. If the pulp becomes necrotic in a tooth with an immature apex, endodontic treatment can be performed using an artificial barrier technique. Mineral trioxide aggregate (MTA) has become the material of choice to accomplish this procedure, however, few studies have evaluated its clinical success. The purpose of this retrospective study was to determine the clinical success of ProRoot MTA used as an artificial apical barrier. Twenty patients were included in this study. After approximately one week of Ca(OH)2 treatment, each patient had MTA placed as an apical barrier in a tooth with a single canal and open apex followed by placement of a final restoration. Patients were recalled and evaluated for clinical signs and symptoms and osseous healing. Immediate post-treatment and recall radiographs were evaluated by two endodontists calibrated for use of the Periapical Index (PAI).