Pneumatosis intestinalis (PI) is a relatively rare disease. A 70-year-old man with stage II squamous cell carcinoma of the middle thoracic esophagus was administered cisplatin plus 5-fluorouracil (CF) therapy as neoadjuvant chemotherapy. On Day 14 of the first course of CF therapy, he complained of acute abdominal pain. Computed tomography (CT) revealed PI of the entire colon and a small air bubble in the mesentery. A colonoscopy revealed that there was no finding suggestive of ischemia. Because there was no sign of peritoneal irritation, conservative treatment was selected. On Day 7 after PI diagnosis, CT indicated the disappearance of PI. The patient underwent a radical esophagectomy. Intraoperative laparoscopic findings showed the serosa of the colon to be intact. The patient was discharged without any complications. It is important to take into account that CF therapy may cause PI and that PI can be treated conservatively.