METHODS All patients with rheumatoid arthritis (RA) attending an outpatient rheumatology clinic at a major military medical center over 6 years were included in follow-up for the development and subsequent course of sacral insufficiency fractures. RESULTS Sacral insufficiency fractures developed in 4 of 386 patients. Consistent with the literature, patients were female, elderly, and/or postmenopausal, had severe or long-standing disease, and were taking corticosteroids. The correct diagnosis was initially delayed because radiographs were normal but was later established with bone scan and sacral computerized tomography. Each patient improved with calcitonin and/or physical therapy over time. CONCLUSIONS Patients with RA represent a unique subgroup predisposed to insufficiency fractures because of multiple osteoporotic risk factors. Patients who have RA and acute low back or buttock pain should be evaluated aggressively for sacral insufficiency fractures with bone and/or computed tomography scans regardless of normal plain radiographs.