Background: Trauma is the leading cause of death in young adults, as well as a significant cause of morbidity and mortality in people of all ages. Ultrasonography (US) is a good first imaging modality because it is fast, repeatable, and noninvasive. It can also be achieved at the same time as other resuscitative steps, providing critical information without the time delay caused by radiograph or CT scan execution and interpretation. Objective: To compare the diagnostic accuracy of chest ultrasound with plain chest X-ray in acute assessment of traumatic hemothorax at Emergency Hospital, Mansoura University. Patients and methods: This was a cross-sectional study included a total of 109 patients with polytrauma and conducted at Emergency Medicine Department, Mansoura University from November 2019 to October 2020. Emergency Hospital, Mansoura University is a level one trauma center with about 250,000 visit and 25,000 trauma cases per year. Results: The X-ray findings in the cases included in the study where fracture ribs was detected in 76 cases (69.7%), lung contusions in 28 cases (25.7%), obliteration of costophrenic angles in 17 cases (15.6%) and tension pneumothorax in 38 cases (34.9%). US showed 86.2% sensitivity, 100% specificity, PPV 100%, NPV 95.2% and 96.3% accuracy. X-ray showed 58.6% sensitivity, 100% specificity, PPV 100%, NPV 86.9% and 89% accuracy. Conclusion: Ultrasound has significant value in initial assessment of life-threatening conditions of trauma with acceptable sensitivity and high specificity.