Abstract Operations for intraabdominal abscess were performed in 46 (20 percent) of 230 patients with Crohn's colitis and ileocolitis treated at the Mount Sinai Hospital during the decade 1964 to 1974. Internal and external fistulas, intestinal obstruction, and abdominal mass occurred significantly more often in patients with intraabdominal abscess, while only overt bleeding was significantly less common. Abscesses were equally divided between 23 patients who had undergone previous surgery and 23 cases of spontaneous onset. In ileocolitis, the most frequent site of origin was the terminal ileum with right lower quadrant abscess, as opposed to a sigmoid origin in colitis with presentation in the left lower quadrant. There was no mortality among 24 patients treated with simple drainage, usually for superficial abscess, but enterocutaneous fistulas persisted in 5 of these patients (21 percent). Four of 11 patients (35 percent) died after undergoing bypass or ileostomy diversion. Among the 31 patients surviving either of these procedures, 18 (60 percent) required subsequent resection of the diseased bowel. By contrast, among 11 patients treated with primary en bloc resection plus drainage, there was only 1 death (9 percent) and no abscess recurrence or chronic enterocutaneous fistula formation during a follow-up period of 1 to 4 years. The high mortality rate after bypass may be explained by the more serious nature of the disease and the preexisting deep intraabdominal abscess and postoperative sepsis. Simple extraperitoneal drainage is a safe procedure associated with an extremely low mortality; however, when feasible, resection of the diseased bowel seems to be the treatment of choice for abscess in patients with Crohn's colitis and ileocolitis.