PURPOSE: The aim of this study was to analyze frequencies, types, and treatment results of the undisplaced abduction fracture of the neck of the femur for the prediction of the prognosis. MATERIALS & METHODS: From February 1984 to February 1999, the population was selected from those who were admitted in our hospital with the diagnosis of the fracture of the neck of the femur(96 cases). Among them 34 cases of undisplaced abduction fracture who could be followed minimum 2 years were chosen. The types of initial injury, the degrees of the rotation into valgus, union and the incidences of avascular necrosis of the femur head were analyzed by plain radiographs and medical records. RESULTS: The undisplaced abduction fracture of the neck of the femur were 34 cases(35%) of the whole 96 cases and 33 cases of them had been operated. In all the 34 cases we were able to see the bone union, however in 7 cases(20.6%) the avascular necrosis of the femur head were happened. The incidences of the avascular necrosis is related with the degrees of the rotation into valgus(p=0.004). CONCLUSION: The undisplaced abduction fracture of the neck of the femur is known to the result in good prognosis. According to this study, not a few avascular necrosis of the femur head happened. As a results, although undisplaced abduction fracture regained to be paid intention to the incidences of the avascular necrosis and careful follow-up should be accompanied.