An 84-year-old woman underwent a diagnostic laparoscopy preceding a planned total gastrectomy. A bilateral pneumothorax was diagnosed postoperatively, following an uneventful procedure. The patient's clinical parameters led to the diagnosis of capnothorax, a rare complication of laparoscopic surgery. It is important to be able to differentiate between a capnothorax and a pneumothorax because the treatment is different: a capnothorax can generally be treated conservatively. The perioperative signs and symptoms, physiology and treatment of a capnothorax are discussed in this article.