A blunt duodenal injuries are rare in spite of high-energetic injuries are common in this time. The diagnostic is very difficult not only for the reason of the little experience with this type of the injury but in term of the duodenal anatomic localization too. On the other side just late injury Identification of the retroperitoneal part of the duodenum leads to rapid development of the fatal retroperitoneal phlegmon. The development of the clinical symptoms and results of the paraclinical equipment examinations during blunt injury of the upper abdominal part with consequent perforation of the posterior retroperitoneal segment of the duodenum is well-documented by means of the mentioned case. The development of the retroperitonal phlegmon was not noticed despite of the slight diagnostic delayed and defect in the duodenal wall was treated by suture of the perforation aperture. The early detection of the duodenal injury is necessary premise for the good choice of the adequate surgical treatment.