Objective To explore the results of delayed acetabulum fracture treated with open reduction and internal fixation.Methods Nineteen cases of delayed acetabulum fractures treated by open reduction and internal fixation from September 2009 to October 2013 were analysed retrospectively.Thirteen cases were males and six females,and mean age was 40 years (range,23-67 years).All patients were injured in motor vehicle traffic accidents.There were ten cases of simple fractures (five posterior wall,one anterior wall,one posterior column,one anterior column and two transverse) and nine complex fractures (four posterior column with posterior wall,two transverse with posterior wall,one "T" type,one anterior and posterior column with transverse and one double column) according to the Letournel and Judet classification.Time from injury to surgery was 22-125 days (mean,36 days).Ilioinguinal approach,Kocher-Langenbeck approach or combined approach was used during operation according to the types of fracture.Reduction results were evaluated by the Matta standard and clinical results by the Matta modified D'Aubigne and Postal scoring system.Complications were recorded as well.Results All patients were followed up for 18-37 months (mean,28 months).Bone union was achieved after 3-6 months (mean,3.9 months).According to the Matta standard,six cases were rated as anatomical reduction,ten satisfactory reduction and three unsatisfying reduction.According to the D'Aubigne and Postal scoring system,the clinical results were excellent in thirteen cases,good in two,fair in two and poor in two.There were one cases of femoral head necrosis,six heterotopic ossification,one sciatic nerve injury,two deep venous thrombosis of the lower extremity.Complications included one case of femoral head necrosis,six heterotopic ossification,one sciatic nerve injury and two lower extremity deep vein thrombosis.Conclusion For the delayed acetabular fractures,restoring normal anatomy of the acetabulum and stable internal fixation can receive good clinical results.