Post-traumatic avascular necrosis is a notorious complication of intracapsular fractures of the femoral neck, whether or not the fracture unites. The incidence of avascular necrosis of the femoral head following femoral neck fractures has been reported variably ranged from 7% to 84%. The purposes of this study are to analysis the clinical features of avascular necrosis of the femoral head following femoral neck fractures and to define causative factors of posttraumatic avascular necrosis. From May 1986 to May 1995, sixty-eight patients with intracapsular femoral neck fracture were operated on osteosynthesis in soonchunhyang University Hospital; we analysed retrospectively with follow-up more than two years, post-traumatic avascular necrosis(AVN) was developed in 13 patients(AVN group) and united forty-six patients were included non-avascular necrosis group, nine patients were excluded due to nonunion. Comparative study was performed between these two groups. The results were as follows: 1. The avascular necrosis of the femoral head following femoral neck fractures treated with osteosynthesis was noted in 13 cases (19%) 2. The eleven cases of 13 cases showed segmental collapse of the femoral head within 2 years. 3. Among the causative factors, age and sex, delay before operation and fixation device have no statistical significance(p>0.05) but type of fracture, initial displacement and quality of reduction showed to be statistical correlation(p<0.05). In conclusion, adequate reuction and internal fixation for the femoral neck fracture may essential to minimize avascular necrosis following osteosynthesis.