PURPOSE: We performed a retrospective study of completely displaced supracondylar fracture of humerus in children to evaluate the result of primary open reduction and internal fixation for this injuries, and also to know whether it is recommendable or not for such injuries. MATERIALS AND METHODS: For 5 years duration from March '96 to Feb. '01, we treated 58 cases of completely displaced supracondylar fractures of humerus in children. Among them we performed primary open reduction and internal fixation of this fracture in 14 cases. We followed up those cases more than 18 months and evaluated the results by Flynn et al. and Mark et al. criteria. RESULTS: Eleven of them resulted in excellent grading by both Flynn and Mark criteria. Three cases not involved in excellent grading proved to be good result by Mark criteria. But by Flynn criteria, 2 cases showed good results and the other one proved to be fair. In all cases, the patient and parents were satisfied cosmetically and functionally. Only in one case, the recorded grading was different, fair by Flynn and good by Mark criteria. CONCLUSION: Primary open reduction and internal fixation in the treatment of completely displaced and not easily reduced supracondylar fracture of humerus in children resulted excellent and good results with few complications, and patients were satisfied with the results functionally and cosmetically. So we recommend proceeding to primary open treatment and internal fixation for these difficult fractures with low threshold to open reduction.