Pneumatosis cystoides intestinalis is a rarely seen disease characterized by cysts filled with multiple gases in the wall of the small or large intestine. Many factors have been suggested in the etiology and pathogenesis, including peptic ulcer, pyloric stenosis, and endoscopic trauma. Because various clinical characteristics and symptoms are observed together, diagnosis is generally difficult. It may be a cause of free air observed on direct radiographs. Treatment is directed at the cause and although there is generally a good course, it can sometimes lead to severe complications. In this paper, we present the case of a 33-year old male being prepared for surgery for pyloric stenosis due to a peptic ulcer. In the preoperative tests, because acid was determined within the abdomen and free air below the diaphragm, pneumatosis cystoides intestinalis was considered in the differential diagnosis. Definitive diagnosis was made during the operation and surgical treatment was applied.