An experimental study on the effect of the induced avascular necrosis of the femoral head on the femoral anteversion was made in the hips of 74 three to four-week-old rabbits. The results were as follows; l. In 18 of the 74 operated rabbits, a relative increase of anteversion was observed on the operated side, as compared with the nonoperated femur, the differences ranging from 10 to 75°(average increase was 25.9°). 2. Anteversion increase was actually internal rotation of femoral shaft starting from the subtrochanteric level and progressively increasing downward with spiral fashion. 3. The cause of anteversion increase was not proved in this experiment, but anteversion increase was a result of avascular necrosis.