Acute ileal diverticulitis (ID), a diagnosis traditionally made during emergent surgical exploration, is usually mistaken for appendicitis or other acute intestinal or extraintestinal right lower quadrant events. A correct preoperative diagnosis could potentially avoid surgery or optimize operative timing. Four subjects (mean age 63 yr, range 49-77 yr; 2 male/2 female) were seen with acute ID from 1994-1996 and were diagnosed and managed using contemporary algorithms. The presentation included abdominal pain (1-4 days duration; all subjects), leukocytosis (3 subjects), fever (1 subject), and physical findings indicative of an acute right lower quadrant process without overt peritoneal signs (all subjects). CT scanning in each instance showed inflammatory changes focused around the ileocecal region without abscess. The scans could not differentiate colonic from noncolonic disorders; a distinct colonic mass was strongly suspected in one case. Colonoscopy performed in the acute setting confirmed the absence of colonic neoplasm, acute colitis, typical findings of appendicitis or inflammatory bowel disease. The procedure was tolerated well in each case without complication. Following colonoscopy, the diagnosis of diverticulitis (ID or colonic) was suspected; the patients were treated conservatively with antibiotics and temporary bowel rest; and the inflammatory findings resolved. Subsequent barium studies (upper gastrointestinal series with small intestinal follow-through) performed during the remitted interval confirmed the presence of multiple terminal ileal diverticula in each case and no other abnormalities. Two of the patients developed recurrences of acute ID in follow-up (1 patient at 2 months; 1 at 6 and 12 months). Both of these subjects eventually underwent uncomplicated nonemurgent ileocolonic resection with the correct preoperative diagnosis of ID. Two other subjects have had no recurrence (at 4 and 24 months of follow-up). No serious adverse event occurred from conservative management, each patient responded promptly to this approach, and the diagnosis was rapidly suspected and confirmed in those subjects who recurred. CONCLUSIONS: ID can be suspected and diagnosed without emergency surgical exploration by using colonoscopy to clarify CT scan findings. This diagnostic approach allows for conservative, expectant management reserving surgery for recurrence, for complication, or for an interval period following resolution of the inflammatory reaction. In our small patient series treated without initial resection, delayed recurrence with a variable interval of complete remission was commonly associated with the condition.