The orthodontic mini-implant (MI) is a widely used anchorage device in orthodontic treatment. This prospective study analyzed MI survival and factors associated with MI survival in 139 patients (114 females and 25 males; average age, 25.7 years; age range, 12-56 years) who had received orthodontic treatment with MIs. Survival analysis and Kaplan-Meier curves were used to identify clinical variables associated with MI survival. For the 254 MIs investigated, the overall success rate was 85.8%, and the 1-year cumulative survival rate was 81.6%. MI survival was significantly associated with patient age and MI size. Notably, MI survival was significantly longer in patients aged 20-30 years than in older patients. The Cox proportional-hazards model revealed a 5% increase in failure risk for every 1-year increase in age among participants older than 30 years. Additionally, MI failure risk was inversely associated with MI length. MIs are generally reliable anchorage devices for orthodontic treatment but should be used with caution in older patients, due to the higher rate of failure in that population. Another important factor in MI survival is implant size. Future studies should attempt to clarify associations between MI survival and clinical variables.(J Oral Sci 58, 515-521, 2016).