Early stage osteonecrosis of femoral head is a major therapeutic dilemma in orthopedics. Many joint preserving treatment modalities have been proposed, but none of them is entirely satisfactory. Among them, core decompression has been widely performed. The results of twenty two core decompression procedures that were performed for osteonecrosis of the femoral head in fifteen patients were retrospectively reviewed to evaluate the effectiveness of the procedure. From January 1990 to December 1993, we had treated twenty two cases of the osteonecrosis of femoral head. The average follow-up was 31 months, ranging from 12 months to 58 months and the average age at operation was 39.6 years, ranging from 21 to 58 years. By Ficat-Arlet stage, the stages I were 1 case,IIa 6 cases, IIb 7 cases and III 8 cases. The functional and radiological evaluation was done preoperatively and at final follow up by the Harris Hip score and Ficat stage. The results were as follows. The improved cases were 10 cases and the progressed were 12. Radiologically, none of 1 hip(0%) with stage I, two of 6 hips(33%) with stage IIa, four of 7 hips(57%) with stage IIb, and six of 8 hips(75%) with stage III have progressed. Mean preoperative Harris Hip score was 57 points and it improves to 69 (the improved 13 cases; 85, the progressed 9; cases; 49)at final follow up. In six of the progressed 9 cases, the arthroplasties were performed. Among them, five cases are being observed. In conclusion, the core decompression is not only highly effective in preventing further change in femoral head, but also relieving pain and delaying time for arthroplasty at late stage osteonecrosis of femoral head.