One hundred fifteen hips in 87 patients with non-traumatic avascular necrosis of the femoral head (ANFH) (men, 54; women, 33) (steroid induced, 49; alcoholic, 21; idiopathic, 17) were radiologically classified into six distinct types (Types 1A, 1B, 1C, 2, 3A, and 3B) based on the following: (1) the size and location of the necrotic area in relation to the weight-bearing surface of the acetabulum as seen on anteroposterior views in the standing position and (2) initial roentgenographic abnormalities. The natural course of the disorder in each group were observed for more than two years (range, two to 18 years; mean, five years). Of the 79 hips without collapse of the femoral heads (Stage II) at the beginning of follow-up evaluation, 42 femoral heads subsequently collapsed. These collapses took place predominantly in cases involving Types 1C, 2, and 3B. Conversely, the incidence of collapse was significantly low in the other groups (Types 1A, 1B, and 3A). Collapse of the femoral head occurred in 78 femoral heads of 115. The incidences of collapse by group was 0% for Type 1A, 19% for Type 1B, 94% for Type 1C, 100% for Type 2, 12% for Type 3A, and 100% for Type 3B. These data indicate that this radiologic classification of necrosed femoral heads is useful for evaluation of the risk of collapse or for prognosis of the affected hip joints as well as for choosing an appropriate treatment modality, either conservative or surgical, during the early stages of ANFH.