Pneumoperitoneum (PP) is usually the result of perforation of the gastrointestinal (GI) tract with associated peritonitis. However, other rare causes, including spontaneous PP incidental to intrathoracic, intra-abdominal, gynecologic, and miscellaneous other origins not associated with a perforated GI tract have been described in the literature. Six cases of PP without any perforated GI tract are reported. Three patients with generalized peritonitis underwent exploratory laparotomy or laparoscopy when clinical examinations suggested an acute abdomen. At surgical procedure, perforated pyometra, perforated liver abscess and a ruptured necrotic lesion of a liver metastasis were documented in these patients, respectively. We also saw 3 PP patients not associated with peritonitis. Two patients with PP caused by pneumatosis cystoides intestinalis were encountered, 1 was managed conservatively and the other received diagnostic laparoscopy. A patient in whom pneumomediastinum and pneumoretroperitoneum were accompanied by PP caused by an alveolar rupture based on decreased pulmonary compliance due to malnutrition was managed conservatively. The history of the patient and knowledge of the less frequent causes of PP can possibly contribute towards refraining from exploratory laparotomy in the absence of peritonitis.