The majority of patients with acute diverticulitis can be managed medically. Some will have a complication of diverticulitis such as free perforation with peritonitis, abscess formation, obstruction, or fistula formation. Perhaps even a larger number will develop recurrent diverticulitis, which is associated with an increased rate of complications. Although the preoperative diagnosis of these problems may be obvious in many patients, elderly or steroid-treated patients may have few manifestations of significant intra-abdominal disease. Of extreme importance in the management of these complications of diverticulitis is the preoperative resuscitation. Intravascular volume depletion is replaced with intravenous fluids, and intravenous antibiotics are given. At this time, with any of these complications, it is unusual to perform the classic three-stage operation, which includes an initial diverting colostomy and drainage followed by resection of the involved colon and, finally, a colostomy closure as the third stage. The usual treatment now is a two-stage operation with the initial operation being resection of the diseased segment and formation of a colostomy proximally and either a mucous fistula or a Hartmann's pouch distally. The second stage is the colostomy closure. This two-stage approach is indicated in patients with acute diverticulitis complicated by perforation, whether free or confined with abscess formation, and in patients with obstruction or fistula formation in whom a preoperative bowel preparation is not possible. Resection and primary anastomosis should not be performed in the elderly in the emergency setting for complicated diverticulitis. However, this is the procedure of choice in the elective treatment of diverticulitis and its complications in the elderly.