The etiology and treatment of the ischemic necrosis of femoral head continue to be controversial and the pathogenesis remains obscure. It has been generally accepted that the lesion is secondary to vascular obstruction and that osseous tissue dies and undergoes structural collapse. A standard radiograph cannot help with early diagnosis of femoral head osteonecrosis, and magnetic resonance imaging (MRI) is known to be suited to the diagnosis of early stage of femoral head osteonecrosis. The aim of treatment of avascular necrosis of the femoral head must be to preserve, not to replace, the femoral head. Among the various operation methods for osteonecrosis, core decompression is believed to promote revascularization and relieve pain with similar effect of fascial release for a muscle compartment syndrome. The authors had treated 16 hips of osteonecrosis which is early stage by Ficat and Arlet classification (stage I, IIA) with core decompression and also 5 hips of osteonecrosis (stage IIB, III) for relief of pain and for delay of reconstructive operation from April, 1990 to February, 1992. The results were following. 1. There were eleven men (73%) and four women (27%) and the ages ranged from 19 to 55 with an average of 42 years old. 2. MRI and bone scanning were performed in all cases, and Mitchell classification was applied to MRI findings of femur head osteonecrosis (class A: 7 hips, class B: 8 hips, class C: 3 hips, class D: 3 hips). MRI was especially valuable in early diagnosis of femoral head osteonecrosis. 3. There were 7 stage I, 9 stage IIA, 3 stage IIB and 2 stage III according to Ficat and Arlet classification. 4. Clinically by Ficat criteria, very good and good results were obtained in 86% of stage I, 78% of stage IIA and 33% of stage IIB. Fair and failure results were obtained in 100% of stage III. Radiographically by Ficat criteria, 71% of stage I and 67% of stage IIA were very good and good result, One hundred percent of stage IIB and 100% of stage III were fair and failure result. 5. The diagnosis of osteonecrosis in early stage is essential, and core decompression is effective in the treatment of early stage (I or IIA) of osteonecrosis of femoral head in adult.