Aseptic osteonecrosis is due to local hypoxemia related to the sickling process. Its frequency in the U.S.A. is 8,5 p. 100 for heterozygotic patients and 0,2 p. 100 for homozygotic ones. It is rare in AS status but frequent in the double heterozygotism SC. Alcoholism, hyperlipidemia, hyperuricemia, cortisonic treatments and pregnancy are facilitating factors. For vascular causes the femoral epiphysises are most often affected. Radiological features are described.