Objective To evaluate the operative procedure and the cl inical effectiveness of open reduction and internal fixation in the treatment of posterior malleolus fractures. Methods Between June 2005 and December 2008, 46 patients with posterior malleolus fractures were treated with open reduction and internal fixation and followed up. There were 29 males and 17 females with an average age of 47.7 years (range, 19-76 years). Fractures were caused by sprain in 17 cases, by fallingin 15 cases, by traffic accident in 12 cases, and by other reasons in 2 cases. The locations were left ankle in 25 cases and right ankle in 21 cases. There were 6 simple posterior malleolus fractures, 13 lateral and posterior malleolus fractures, and 22 trimalleolar fractures, and 5 lateral and posterior malleolus fractures accompanying by injury of deltoid l igament of ankle. According to Lauge- Hansen classification system, 13 cases and 9 cases were rated as supination-external rotation type III and type IV respectively, and 18 cases as pronation-external rotation type IV. According to Naoki’s classification of posterior malleolus fractures, there were 29 cases of posterolateral-obl ique type, 11 cases of medial-extension type, and 6 cases of small-shell type. Seven patients underwent emergency operation and 39 patients underwent selective operation. Results Two patients developed superficial infection, which was cured after dressing change, and the other incisions healed by first intention. Forty-six patients were followed up 37 months on average (range, 18-63 months). All fractures healed after 3 to 6 months (mean, 4.3 months). One patient developed lateral suralcutaneous nerve injury, and 9 patients had mild weight-bearing pain or discomfort. The results of American Orthopaedic Foot and Ankle Society (AOFAS) ankle and hindfoot score were excellent in 17 cases, good in 21 cases, and fair in 8 cases with an excellent and good rate of 83%. The mean visual analogue scale (VAS) score was 1.9 (range, 0-5). Conclusion The anatomic reduction and internal fixation can achieve the satisfactory results in the treatment of posterior malleolus fractures. The best treatment and fixation methods should be chosen based on different types of posterior malleolus fractures.