A complete review was made of seventy-seven cases of non-traumatic avascular necrosis of bone in patients treated with corticosteroids seen at the Mayo Clinic from 1950 to 1968. The single common finding was treatment with corticosteroids in dosages greater than physiological replacement for long periods either continuously or intermittently. Serum lipids were abnormal in the majority of cases so studied. Roentgenograms showed characteristic segmental avascular necrosis followed by varying degrees of collapse and secondary degenerative changes. Gross and histological study of surgically removed femoral heads confirmed the diagnosis of avascular necrosis. Intravascular fat emboli were noted in a significant number of femoral heads removed from corticosteroid-treated patients with avascular necrosis.