Six cadavers were used to define the projection of the external iliac artery on the inner table of the acetabulum, and to quantitatively determine bony dimensions of the danger zone with regard to screw placement. The results showed that the majority of projections of the external iliac arteries were located on the superior portion of the posterosuperior quadrant and extended to the mid-superior portion of the anterosuperior quadrant (danger zone). The inferior portion of the danger zone was relatively far from the external iliac artery. The greatest depths of bone were found in the inferior portion of the danger zone, and the depths of bone in the middle and superior portion of the danger zone were relatively thinner. This anatomic study showed that the real danger zone was found in the middle and superior portions of the anterosuperior quadrant of the acetabulum. The inferior portion of the anterosuperior quadrant was relatively safer. This area may be considered if transacetabular screw replacement in the anterosuperior quadrant is required.