Cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) have been proven to be an effective treatment modality for selected patients with peritoneal surface malignancies. The most common surgical complications after CRS and HIPEC are anastomotic leakage, intestinal obstruction and peripancreatitis. This case report presents two patients with early and late postoperative diaphragmatic hernia after CRS and HIPEC. One patient that initially had pseudomyxoma peritonei complained of persistent chest pain and dyspeptic disorder after peritonectomy and HIPEC and underwent reoperation due to a left diaphragmatic hernia containing the splenocolic flexure. The other patient had gastric cancer and peritoneal carcinomatosis and developed anastomotic leakage of the transverse colon anastomosis and pleural empyema. Stripping of the diaphragm is often performed during CRS, sometimes combined with diaphragmatic resection. A herniation through a diaphragmatic defect is rarely diagnosed during either the early or late postoperative period. Direct suture of the defect or closure with synthetic or biological tissue are possible surgical techniques for repair with a good prognosis.