Usually the condition of ipsilateral fracture of femur and tibia is called floating knee, it is termed applied to the flail knee joint segment. The key point of the treatment is focused to the early restoration of the knee function. We experienced 86 consecutive cases during the period from March 1978 to February 1991 in Yonsei University Wonju College of Medicine. Among them, 51 cases(above 16 years old) were analysed with the mean follow up period of 2.1 years(1.2-5.6 years). The results obtained were as follows: 1. Main cause of these fractures is traffic accident. Among them, the pedestrian accident is more than in-car accident. 2. The cases of open fracture were 13 cases (25.5%) in femur and 31 (60.8%) in tibia. The degree of open fracture was more severe in tibia. 3. There were 2 cases (3.9%) of fat embolism syndrome preoperatively. 4. At an average 25 months follow up after injury, the good and excellent result of the group 1 and 3 was 85.2%, and the group 2 and 4 was 71.4% by Karlström and Olerud criteria. 5. At the last follow up examination, the mean loss of range of motion of the knee was 5.6° in group 1 and 3, 10.9° in group 2 and 4(P<0.05). 6. The operative treatment of the both side is better than case of one side operation and other side conservative treatment.