The results of closed and open reduction via posterior approach with percutaneous pinning of posteromedial displaced supracondylar humerus fractures in children were evaluated. Fifty-five consecutive patients with Gartland type III fractures were reviewed. The mean follow-up period was 22 months (12-48 months). The closed reduction group consisted of 32 patients and the open reduction group with the posterior approach using the triceps-sparing method consisted of 23 patients. Both groups were stabilized with cross Kirschner wire fixation and followed the same protocol. In comparison with closed reduction, despite the fact that better bone alignment was obtained with open reduction, longer union time (7 vs. 5.8 weeks), significantly reduced range of motion of the elbow (12.3 degrees vs. 3.8 degrees), poorer functional outcomes and bad cosmetics because of hypertrophic scar tissue of the skin were found. The patients were analyzed according to their Bauman angle and Flynn criteria: good or excellent functional and cosmetic results were 91% in the closed reduction group but 52% in the open reduction group. On the basis of results of this study, closed reduction and percutaneous fixation of the posteromedial totally displaced fractures are preferable to open reduction with posterior approach.