We reviewed 205 hips (in 151 patients, 125 men and 26 women) which were diagnosed osteonecrosis of femoral head and treated with bipolar endoprosthesis from 1985 to 1993 in Seoul National University Hospital to delineate the efficacy and indication of use of bipolar endoprosthesis in osteonecrosis. They were followed up for an average of 56 months (16 to 100 months). The mean age at operation was 44 years (21 to 84 years). The types of prosthesis used were as follows : Omnift (107), AML (57), Harris-Galante (19) and others (22). The preoperative Harris hip score improved from 49 points preoperatively to 89 points at last follow-up. The pain score improved from 18 points to 39 points, activity score from 9 points to 12 points and gait scare from 19 points to 31 points. The improvement pattern of activities and gait was converse, but that of pain was diverse. One hundred and seventy-eight hips (87%) were satisfactory (Harris hip score : more than 80 points) and 27 (13%) were unsatisfactory. Radiologic findings of last follow-up showed stable bony fixation in 186 hips (91%), stable fibrous fixation in 12 hips (6%) and unstable fixation in 7 hips (3%), Ten migrations of prosthesis were noted: cup migration 5 (2.4%) and stem sinking 5 (2.4%). Heterotopic ossification was noted in 9 (4.4%). Osteolysis in acetabular side was observed in 6 (3%) and in femoral side, 22 (11%). Complications were as follows : 4 stem loosening (1.9%), 5 fixed varus position of cup (2.4%) and 1 dislocation of cup (0.5%). Revision was performed in 4 (1.9%) and the causes were 1 infection, 1 protrusio acetabuli, 1 stem loosening and 1 cup dislocation. In conclusion, biopolar endoprosthesis generally gave good results. However, the improvement of pain was unpredictable. Increasing tendency of osteolysis was noted with increasing follow-up duration. Long-term follow-up is mandatory for the accurate determination of osteolysis.