OBJECTIVE To investigate the incidence and etiologic factors of pelvic fractures following radiation therapy for endometrial carcinoma. METHODS Tumor registry and radiation oncology records of patients treated for endometrial carcinoma at The Toledo Hospital between April 1989, and December 1992, were reviewed. Patients identified as having pelvic fractures without the presence of metastatic disease underwent total body mineral density measurement with dual x-ray densitometry. RESULTS Two of 75 patients (2.7%) were found to have pelvic fractures an average of 29 months from the completion of postoperative irradiation. One patient, who received preoperative irradiation, was also identified as having developed a fracture of the pelvis and was included in the analysis. All patients were treated prone with 10-15 MV photons in four fields daily. All three fracture patients received 45 Gy external beam radiation therapy. The two postoperative patients each received a single vaginal brachytherapy application delivering 20 Gy to 0.5 cm deep to the vaginal mucosa with a vaginal cylinder containing 30 mgRaeq 137Cs. The preoperative patient received a single brachytherapy application with tandem and colpostats delivering 20 Gy to point A. Only one of the three fracture patients had the entire pubis included in the field of external beam treatment. One patient was taking nonsteroidal anti-inflammatory medication, one patient thyroid hormone replacement, and one patient was taking both types of medication. CONCLUSIONS The etiology of pelvic fractures after irradiation is multifactorial. A complete medication history should be obtained, and care should be exercised in positioning the radiation fields to avoid inclusion of the entire pubis prior to the initiation of the radiation treatment.