Most patients with diverticulosis have few or no symptoms. The diverticulosis condition in these individuals is found incidentally during tests for other intestinal problems. Twenty percent of patients with diverticulosis condition will develop symptoms related to diverticulosis. The most common symptoms of diverticular disease include abdominal cramping, constipation, diarrhea and bloating. These symptoms are related to difficulty of passing stool along the left colon narrowed by diverticular disease.

More serious complications include diverticulitis, collection of pus (abscess) in the pelvis, colon obstruction, generalized infection of the abdominal cavity (bacterial peritonitis), and bleeding in the colon.

A diverticulum can become infected with bacteria and ruptures, causing diverticulitis. Fever, and pain and tenderness of the lower left abdomen are common symptoms. Constipation or diarrhea may also occur. A collection of pus can develop around the inflamed diverticulum, leading to formation of an abscess, usually in the pelvis. On rare occasions, the inflamed diverticula can erode into the urinary bladder, causing bladder infection and passing of gas during urination. Inflammation in the colon can also lead to bowel obstruction. Infrequently, a diverticulum ruptures freely into the abdominal cavity causing a life threatening infection called peritonitis.

Diverticular bleeding occurs when stool erodes into a blood vessel at the base of a diverticulum. Rectal passage of red, dark or maroon-colored blood and clots occur without any associated abdominal pain. Rarely, blood may be black in those bleeding from a diverticulum of the right colon. Bleeding may be continuous or intermittent, lasting several days. Patients with active bleeding are usually hospitalized for monitoring. Intravenous fluids are given to support the blood pressure. Blood transfusions are necessary for those with moderate to severe blood loss. In a rare individual with brisk and severe bleeding, blood pressure can drop, causing dizziness, shock, and loss of consciousness. In most patients, bleeding stops spontaneously and they are sent home after several days in the hospital. Patients with persistent, severe bleeding require surgical removal of the bleeding diverticula.