Pneumoperitoneum, usually seen as free air under the diaphragm, is a finding that can be seen on plain abdominal radiographs, signifying a leakage of air, usually from a perforation in the gastrointestinal tract. There are several other potential pathways from other body compartments for air to enter the abdominal cavity. Pneumoperitoneum does not always signify bowel rupture, as it can also result from pneumomediastinum and pneumothorax, and in patients who are being mechanically ventilated. Patient history and physical examination can assist in a preliminary diagnosis before diagnostic imaging. Plain chest/abdominal radiograph or computed tomographic scan of the abdomen can be diagnostic of pneumoperitoneum. Surgical versus nonsurgical conservative observation is determined on the basis of the cause and amount of free air.