Retroperitoneal and mediastinal emphysema after colon resection is extremely rare, especially in the absence of anastomotic leakage. The feasibility and safety of conservative treatment for this complication are unknown. We report a patient who underwent open sigmoid colon resection for colon cancer and developed retroperitoneal and mediastinal emphysema that was not caused by anastomotic leakage. Retroperitoneal and mediastinal emphysema occurred as a result of diverticular perforation. We were able to treat this patient successfully with conservative management.