Intra-abdominal abscess in regional enteritis. Intra-abdominal abscess (IAA) developed in 129 of 610 patients (21.2%) with Crohn's disease confined to the small bowel. The location of the abscess was intraperitoneal (IPA) in 109 (17.9%) and retroperitoneal (RPA) in 20 (3.3%). There was a marked preponderance of male patients in the retroperitoneal group (ratio, 18:2) (p less than 0.0001). All 129 patients were operated on. Thirteen of one hundred nine patients (12%) with IPA were reoperated on for recurrent abscess, and nine (8.2%) for other reasons. External fistula developed in 24 patients (22%) after simple incision and drainage. Four (3.7%) died; one from hepatitis, and three from sepsis 5, 14, and 90 days after surgery. Of the 20 patients with RPA, two (10%) were reoperated on for recurrent abscess and four (20%) for other reasons. External fistula developed in two patients (10%). There were no deaths in this group. A small number of patients with IAA complicating regional enteritis had persistent sepsis causing postoperative death, which is, however, six times lower than in our comparable series of Crohn's (ileo)colitis. 