Anastomotic defect after colorectal surgery usually presents with clinical and biochemical signs and is confirmed by radiological studies. We report a rare case of anastomotic defect in the form of pneumomediastinum. The patient had no clinical signs of leakage, and no defect was found during acute laparotomy, performed because of wound dehiscence after the primary operation. Pneumomediastinum was found by chest radiography. Radiological examination of the colon with water-soluble contrast confirmed the leakage, and laparotomy revealed an anastomotic defect retroperitoneally.