Objective: To evaluate the clinical outcomes of immature teeth treated with regenerative endodontic procedures with an over-36-month review, to identify potential contributing factors of root deve-lopment, and to provide new reference for long-time prognosis of regenerative endodontic procedures. Methods: We recruited teeth that had undergone regenerative endodontic procedures at the Department of Pediatric Dentistry in Peking University School and Hospital of Stomatology from January 2013 to June 2017 and had a follow-up period of more than 36 months.Clinical and radiographic records were collected.We evaluated the treatment outcomes and summarized different patterns of root development.Changes in root length, root canal wall thickness were compared between preoperative and recall radiographs.A statistical analysis was performed using software SPSS 22.0 to identify potential contributing factors of root development. Results: In this study, 84 teeth were recruited and the mean follow-up period was (44.7±19.3) months.The longest follow-up period was 81 months.Sixty-eight teeth (81.0%) were clinical success with bony healing, and 55 teeth (80.9%) gained the continued root development.Forty teeth completed root development with apical closure.The rate of the apical closure reached 58.8%.Twenty-four teeth gained normal root morphology with the increasing of root length and canal wall thickness and apical closure.The rate of continued root development was 92.5% in teeth with broken central cusp and 58.3% in teeth with trauma, which was statistically significant (P < 0.05).There was a statistically significant difference (P < 0.05) between the root development rates of teeth with different induced bleeding heights (orifice/middle/tip of the root)(92.9%/81.0%/63.2%). Conclusion: Most of the teeth treated with regenerative endodontic procedures achieved continued root development with an over 36-month follow-up.However, the patterns of root development were different.The morphology of some teeth were close to the physiological state.Etiology and the height of induced bleeding are two factors significantly associated with the rate of the continued development root.