Giant colonic diverticulum is a rare complication of colonic diverticulosis. It typically occurs as a single diverticulum located on the antimesenteric border of the sigmoid colon. The most widely accepted theory for its development attributes the progressive dilation to a "ball-valve" mechanism, allowing air to enter but not to exit. Patients usually present complaining of abdominal pain and/or an abdominal mass, although they may remain asymptomatic. Physical examination reveals a tympanic abdominal mass that appears as a round radiolucency on plain radiographs and CT. Barium enema demonstrates the relationship of the diverticulum to bowel and may document communication with the colonic lumen. To alleviate symptoms and prevent complications, the recommended treatment is excision of the diverticulum in continuity with the involved colonic segment. We report a case and discuss the presentation, diagnosis, and management of giant colonic diverticulum.