Bone graft harvest site fracture can occur after removal of bone from the anterior iliac crest. No biomechanically proven guidelines for safe removal of bone exist. Cadaveric hemipelves were tested in a materials testing system machine, with the harvest site occurring 15-mm posterior to the anterosuperior iliac spine in 8 specimens and 30-mm posterior in 7 specimens. These pelves were then tested to failure by simulating avulsion fractures caused by the forces of the flexors of the hip. Average force at failure was 783 N (standard deviation, +/- 333 N) in the 15-mm group and 1917 N (standard deviation, +/- 735) in the 30-mm group. This study provides objective data which demonstrate that harvest 30 mm posterior to the anterosuperior iliac spine weakens the iliac crest less than harvest 15 mm posterior to the anterosuperior iliac crest. To minimize the possibility of iliac crest fracture after bone graft harvest, bone should be removed at least 30 mm from the anterior superior iliac spine.