Background and purpose: Monteggia fractures can be problematic injuries. The aim of this population-based study is to evaluate the risk of complications according to the Bado types, clinical outcome, and incidence.Methods: 72 children (median age 6, range 2–11 years) with 73 Monteggia fractures treated during 2014–2022 were identified from the institutional fracture register. Timing of diagnosis, complications, and method of treatment were registered. Outcomes were assessed at mean 4 years (1–9) follow-up in 68 (94%) children. The census population (< 16 years old) in Helsinki metropolitan area during the study period was assessed.Results: Bado types I (n = 43) and III (n = 27) comprised all but 3 of the fractures. Diagnosis was made on admission in 57, and with a 1–8-day delay in 16 children. 8 children had sustained an associated nerve injury. 35 children were treated operatively, 7 after failed closed treatment. 4 reoperations were performed, including 3 ulnar osteotomies. The risk of complications (odds ratio [OR] 4.9, 95% confidence interval [CI] 1.7–14) and closed treatment failures (OR 12.3, CI 1.3–118) was higher in Bado type III than in type I injuries. 60 children attended for clinical follow-up, all had congruent radio-humeral joints and full range of elbow and forearm motion. Mean PedsQL was 94 (72–100) and QuickDash 3 (0–13). 8 additional children reported normal elbow functions by phone. The calculated mean annual incidence of Monteggia injuries was 2.9/100,000 children.Conclusion: Monteggia fractures are rare (2.9/100,000 yearly). Bado type III injuries are associated with a high risk of complications.