Pneumoperitoneum is generally due to gastrointestinal perforation and need emergency laparotomy. We report three cases of pneumoperitoneum without definite cause. A six month old infant, who had ventriculoperitoneal shunt in place and on mechanical ventilation, was conservatively treated for pneumoperitoneum, and recovered. Two newborns underwent emergency laparotomy with diagnosis of perforation peritonitis; but no gastrointestinal pathology was found at operation. In one of them features of ruptured meconium-cyst could be found. All patients survived. The causes of idiopathic pneumoperitoneum are analysed.