The anteroposterior radiographs of 50 patients with multiple fractures of the pelvic ring were analyzed and the findings compared with the interpretation made at the time of admission. Thirty-six of the 50 patients (72%) had associated sacral fractures. Sixty-one percent of the sacral fractures had been missed on the initial examination. Disruption, displacement, deformity, and density changes of the sacral arcuate lines are described as signs of sacral fracture.