Background: Patients with CD have a lifetime risk of 80-90% for undergoing surgery due to their disease. Many of these patients are set on immunosuppression [IS] at the time point of surgery. Serious side-effects of IS are wound complications, which have been shown in solid organ transplantation both in clinical trials and in animal models. Aim of this study was therefore to evaluate the rates of post-surgical complications after abdominal surgery for CD in patients with or without perioperative IS (steroids [S] or azathioprine [A]).Methods: We retrospectively analyzed 484 consecutive abdominal operations in 374 patients with CD from January 1995 until June 2008 (152♂, 222♀, 39.1±7.9 years). We focused on the following post-surgical complications: Wound infection, pneumonia, urinary tract infection, thrombosis/embolism [M = major complication], surgical revision [M], anastomotic leakage [M], intraabdominal abscess [M] or death [M]. Furthermore, we analyzed the following sub-groups: rectal resection, colonic resection or small bowel resection.Results: There were 69 rectal resections, 137 colonic resections and 172 small bowel resections. 241 operations (=49.8%) were performed under perioperative IS. The overall complication rate [OCR] was 18.6% (n=90), the major complication rate [MCR] was 8.7% (n=42) and the anastomotic leakage rate [ALR] was 3.3% (n=16). There was no significant difference between patients without immunosuppression [-IS] compared to those with either steroid [+S], azathioprine [+A] or combined [+SA] medication (OCR: -IS 17.7%, +S 20.9%, +A 13.5%, +SA 19.6%; MCR: -IS 7.0%, +S 11.8%, +A 5.4%, +SA 9.8%). Also patients with a high-dose steroid-therapy (≥20mg/d) had no increased OCR, MCR or ALR. Patients with rectal or colonic resection had a higher complication rate than patients with small bowel resection, but there was also no increase with IS. However, patients on IS were treated significantly longer inpatiently than those without IS despite same complication rates (17±20 vs. 13±8 days, p=0.01).Conclusion: Patients with rectal or colonic resection for CD have an increased risk for post-surgical complication than patients with small bowel resection. Nearly 50% of the patients undergoing abdominal surgery for CD are on IS during surgery. However, perioperative medication with steroids (even high-dosage) or azathioprine does not alter the post-surgical complication rate in CD patients. Therefore, IS should not be the key factor for decision-making when surgery is performed.