Insufficiency fractures of the sacrum are rare but a distinct subgroup of pathologic fractures characterized by reduced osseous elastic resistance due to structural alterations of the bone. Stress fractures occurring in the settings have been defined as insufficiency fractures. Insufficiency fracture of the sacrum are difficult to diagnose, as plain radiographic findings are either unhelpful or misleadining. Bone scan is very sensitive and shows moderate to high uptake but the characteristic of H-shaped pattern of increased uptake of sacroiliac joint, specific for an insufficiency fracture, is only rarely seen. M.R.I is clearly the examination of choice, as it reveals early medullary edema and frequently a fracture line in a typical location. M.R.I helps in distinguishing tumoral disease from an insufficiency fracture. In this report, two cases of insufficiency fracture of the sacrum are discribed and compared with those previous studies.