Pneumoperitoneum is considered to be a surgical emergency as it nearly always indicates a perforated abdominal viscus. However, in rare cases, the presence of 'free gas under diaphragm' may not imply the need for emergent laparotomy, as pneumoperitoneum can occur without any gastrointestinal leakage. Here we report a rare case of a previously healthy boy with pneumoperitoneum associated with pneumonia and perform a review of the literature to explore the etiological mechanisms and the pathophysiology of non-surgical pneumoperitoneum.