Background: Pelvic fractures are rare but serious injuries. The influence of a concomitant abdominal trauma on the time point of surgery and the quality of care regarding quality of reduction or the clinical course in pelvic injuries has not been investigated yet. Methods: We retrospectively analyzed the prospective consecutive cohort from the multicenter German Pelvic Registry of the German Trauma Society in the years 2003-2017. Demographic, clinical, and operative parameters were recorded and compared for two groups (isolated pelvic fracture vs. combined abdominal/pelvic trauma). Results: 16.359 patients with pelvic injuries were treated during this period. 21.6% had a concomitant abdominal trauma. The mean age was 61.4 ± 23.5 years. Comparing the two groups, patients with a combination of pelvic and abdominal trauma were significantly younger (47.3 ± 22.0 vs. 70.5 ± 20.4 years; p < 0.001). Both, complication (21.9% vs. 9.9%; p < 0.001) and mortality (8.0% vs. 1.9%; p < 0.001) rates, were significantly higher. In the subgroup of acetabular fractures, the operation time was significantly longer in the group with the combined injury (198 ± 104 vs. 176 ± 81 min, p = 0.001). The grade of successful anatomic reduction of the acetabular fracture did not differ between the two groups. Conclusion: Patients with a pelvic injury have a concomitant abdominal trauma in about 20% of the cases. The clinical course is significantly prolonged in patients with a combined injury, with increased rates of morbidity and mortality. However, the quality of the reduction in the subgroup of acetabular fractures is not influenced by a concomitant abdominal injury.