Hollow organ perforation is a life-threatening condition and early diagnosis of perforation is important in improving the prognosis of these patients. The physical phenomenon that then occurs in the abdominopelvic cavum is the presence of extraluminal gas. The basic methods of detecting free gas in the peritoneal cavity are radiological: plain abdominal radiography, ultrasound and computed tomography. In the radiological literature, there is still no clear consensus which technique is optimal for the detection of pneumoperitoneum – plain abdominal radiography, ultrasound or computed tomography. CT is the gold standard for diagnosis but is often preceded by long wait times and unnecessary radiation exposure. Abdominal ultrasound can also be used as an adjunct in decision-making for justifying the risks of transporting a critically ill patient for further imaging. Based on the data presented, it can be assumed that ultrasonography should be treated as the basic method in diagnosing pneumoperitoneum. CT is the gold standard for the diagnosis of pneumoperitoneum, which can also help detect the cause of pneumoperitoneum.