Infraisthmal fracture of the femur is defined as a fracture from just below the isthmic portion to a point about 3 inches above the joint surface of the medial femoral condyle. This study investigated 85 csses of the infraisthmal fracture of the femur admitted at Department of Orthopaedic Surgery, Yonsei University, Wonju College of Medicine from June 1981 to December 1985 with the follow up study. The results obtained were as follows : 1. The sex ratio between male and female was 4.7: 1. Among the 85 cases, mean age of male and female was 30.1 and 39.4 year old respectively. 2. Cabse of fracture was traffic accident almostly. 3. By Reis and Hirschberg Classification, Type 1, 2 and 3 fractures were 28 (32.8%), 36(42.4%) and 21 (24.7%) respectively. 4. Associated injuries were found in 27 patients (31.8%). 5. Ninety three per cent of all cases were treated with internsl fixation by AO principle average 6.7 days after injury. 6. Among the 17 cases of complication, 11 cases were treated with AO technique and autogenous bone graft and one case with electromagnetic field. 7. Eleven cases among the 17 cases of complication were broken plate, non-union, loosening of the screws and etc. These were almostly caused by early weight bearing after discharge.