Background: Pneumoperitoneum is frequently considered one of the commonest surgical emergencies due to its association with gastrointestinal perforation that can result in peritonitis, septic shock, multiorgan failure and death. Accurate and Timely detection of these emergencies is of paramount importance in the management and outcome of the patients. Thus prompt diagnosis is a vital to avoid unnecessary interventions. Objectives: The study aimed to verify the feasibility and usefulness of Ultrasound in the diagnosis of pneumoperitoneum through comparing both Ultrasound and plain radiography findings with the intraoperative findings (the gold standard diagnosis). Methodology: The study was carried out in the Emergency Medicine and Traumatology department at Tanta University Hospitals in the period from September 2019 to September 2021, included eighty three adult patients presented with acute abdominal pain with suspected gastrointestinal perforation. Ultrasound examination was performed by the emergency physician and Plain radiography (erect or lateral decubitus) was done as an important diagnostic tool in acute abdominal pain. All enrolled patients underwent surgical intervention. Results: Sensitivity of ultrasound was higher than that of plain radiography in the diagnosis of pneumoperitoneum (89.39% and 86.63% ) respectively. While plain radiography was more specific than ultrasound (88.24% and 94.12% ) respectively.