In critically injured patients with multiple injuries and unstable pelvic fracture, late mortality almost invariably results from sepsis. We analyzed the clinical features of 11 patients with sepsis caused by soft tissue infections surrounding the fractured pelvis, of 830 patients with pelvic fracture after blunt trauma treated at our level I trauma center over the past 25 years. Soft tissue infection was defined as abscess formation in subcutaneous tissue or muscle diagnosed by computed tomography or an operation. Mean injury severity score was 48, and mean systolic blood pressure on arrival was 66 mm Hg. All patients had multiple concomitant injuries and prolonged hemorrhagic shock. Open pelvic fracture was present in five patients. Mean blood transfusion volume within 24 hours was 12,611 mL. Intra-aortic balloon occlusion was performed in three patients and transcatheter angiographic embolization in nine patients. Embolic sites of transcatheter angiographic embolization were bilateral internal iliac arteries (n = 9), lumbar artery (n = 5), median sacral artery (n = 2), and circumflex femoral artery (n = 2). Infection sites included the gluteal (n = 11), femoral (n = 6), sacral (n = 4), lumbar (n = 4), anterior iliac (n = 2), inguinal (n = 1), and perineal (n = 1) regions. Necrotic changes of infected soft tissue were found in all patients. They underwent open drainage and daily debridement with pulsatile irrigation followed by intravenous antibiotics. All patients developed severe sepsis, five of whom subsequently died of multiple organ failure. In critically injured patients with multiple injuries and unstable pelvic fracture, peripelvic soft tissue infections occasionally cause sepsis. Peripelvic infections are often accompanied by necrotic changes and easily develop into severe sepsis or multiple organ failure. Identifying high-risk patients and early diagnosis with prompt surgical treatment are indispensable for the patients' survival.