Most people will never have any complications from diverticulosis. A few people will have complications. Besides diverticulitis, there may be painless rectal bleeding, a fistula, an abscess, or a bowel obstruction. A fistula is a tunnel going from the colon to another organ, often the bladder. Occasionally, an infected diverticulum may become worse and rupture. If this happens, fluid from the colon can get into the surrounding abdomen, and cause a severe infection. This is a medical emergency, and almost always needs surgery.