Introduction: In the literature the best results for pediatric supracondylar humerus fractures have been achieved by closed reduction and wire fixation. However, in these reports the patient group of open reduction and pinning contained the patients who had had previous ineffective closed reduction trials. This retrospective study compared open and closed reduction with pinning, in which the first group of patients was all consecutively treated with open reduction. Materials and methods: The study included 99 children with displaced extension-type supracondylar fractures of humerus who had complete follow-up. Open reduction patients had not had a previous attempted closed reduction. Open reduction and pinning were performed through a posteromedial incision in the first 44 patients and closed reduction and pinning in the subsequent 55 patients. Mean duration surgery was 15 h with open reduction and 17 h with closed reduction. Mean follow up was 35 months with the open reduction and 21 months with closed reduction. Humeral-ulnar angle was compared to the contralateral elbow, clinical flexion deficiency and extension lag, and complications were evaluated. Results: At the latest follow-up the open group had an average of 5.1degrees valgus change and the closed group 3.6degrees valgus change in humeral-ulnar angle compared to their uninvolved elbow. Average flexion deficiency was 8.61degrees in the open and 5.25degrees in the closed group. Average extension lag was 6.23degrees in the open and 0.6degrees in the closed group. Functional results were satisfactory in 71% of patients in the open and 93% of those in the closed reduction group. Cosmetic results were satisfactory in 95% of both groups. Conclusions: Closed reduction and pinning is superior to open reduction and pinning for the treatment of pediatric supracondylar humerus fractures. In the case of technical insufficiencies open reduction and pinning through a posteromedial incision is an alternative treatment for decreasing the surgical time and complications. Complications was not caused in either group by the delayed surgical timing compared to reports in the literature.