Objective: Intraarticular corticosteroid (IAC) injections are often used to treat temporomandibular joint (TMJ) arthritis associated with juvenile idiopathic arthritis (JIA). One potential complication of IA therapy is heterotopic bone formation (HBF). The purpose of our study was to evaluate risk factors for HBF development in children with JIA who received IA therapy for TMJ arthritis. Methods: This was a retrospective study of children with JIA who had received ≥ 1 IAC injection into the TMJ. Survival regression analysis was performed to identify risk factors for the development of HBF. Results: There were 238 children included, of whom 33 (14%) developed HBF. No cases of HBF were diagnosed prior to the initial injection. Univariate analysis revealed that the risk factors for development of HBF were the total number of injections received into the TMJ and age at diagnosis of JIA, while the length of time from diagnosis of JIA to the first injection was inversely associated with the risk of HBF formation. The total number of injections was no longer significant following adjusted survival models. Children with HBF had increased physical examination evidence of acute or chronic changes, namely decreased maximal incisal opening and increased likelihood of jaw deviation. Conclusion: HBF within the TMJ is relatively common in patients with JIA receiving IAC injections for TMJ arthritis. Future prospective studies are required to delineate the risks posed by the injections themselves as opposed to the underlying disease activity, as well as to evaluate alternative forms of local therapy to the TMJ.