Unstable fractures of the posterior pelvic ring during pregnancy are rare. Pregnancy increases the high demands on the therapy of these types of fractures. The aim of the therapeutic strategy in such a situation is a good functional outcome of the mother without influencing the fetal health. Some osteosynthetic techniques result in good functional outcomes, but they are associated with high amounts of ionizing radiation. We report the case of a pregnant woman who sustained a vertical unstable fracture of the posterior pelvic ring as a result of a traffic accident. The fracture was treated surgically by open reduction and internal fixation with two transiliac reconstruction plates with minimal radiographic exposure to the fetus. One year later, a good functional result concerning the mother was shown. The child was healthy without any signs of prenatal impairment. Surgical treatment of an unstable fracture of the pelvic ring during pregnancy is possible with a justifiable risk to the mother and the child. Consideration of the expected fetal radiation exposure in the course of the therapy is particularly recommended. Using minimal doses of ionizing radiation, the described method results in a good clinical outcome of the mother while simultaneously reducing the radiation exposure of the fetus to an acceptable level.