A few patients who received pelvic radiotherapy have experienced low back pain and presented with various radiographic changes of pelvic bone during the follow up prekid. In these cases, it is important to differentiate diagnoses between insufficiency fracture of pelvic bone and bony metastases. In the present work, we report 5 patients who received radiation for uterine cervical cancer (3), rectal cancer (1), and malignant lymphoma (1) and later developed bone pain and radiographic changes such as insufficiency fracture of the sacroiliac joints, symphysis pubis or acetabulum, osteosderosis, and compression fracture of the lumbar spine. These women were in postmenopausal status. The prescribed external radiation dose ranged from 4500 c㏉ to 5400 c㏉. The patients complained of low back pain which was radiating to leg either immediately after the completion of radiotherapy or up to 14 months after the completion of irradiation. Medical image findings were based on pelvic X-rays, whole body bone scan, CT scan, MRI, and other special radionuctide studies. Those patients with typical radiographic bony changes were treated conservatively with analgesics and bed rest as much as they could. In two cases out of five, the symptoms were subsided or reduced in 3 months and 10 months, respectively. To be aware of such clinical situation is important since it might otherwise be mistaken as symptoms and signs of metastasis. The purpose of this report is to describe the clinical and radiographic characteristics of these cases and to discuss their management.