A colostomy is a surgical procedure that diverts the large intestine to a surgically created opening in the abdomen, called a stoma. Waste exits the stoma into a colostomy bag. This bypasses the lower colon, allowing it to heal from things like cancer, inflammatory bowel disease (IBD), or diverticulitis. When this diversion is no longer needed, surgeons perform a colostomy reversal, reattaching the bowel and allowing waste to pass as it did previously.