The treatment of osteonecrosis of the femoral head is considerably more successful at early stages of the disease, therefore, the diagnosis of osteonecrosis at an early stage is critical for hip preservation. The early diagnosis of osteonecrosis, in turn, depends upon the identification of individuals at risk. Understanding the pathogenic factors leading to osteonecrosis enables the early investigation of at-risk individuals and facilitates prompt diagnosis. The most likely final pathogenic pathway for nontraumatic osteonecrosis involves intravascular coagulation and microcirculatory thrombotic occlusion. Efforts are being made to identify individuals with a heritable tendency to intravascular coagulation who may be at risk for osteonecrosis.