Abstract Background Inflammation of the rectal stump (proctitis) after subtotal colectomy with ileostomy for ulcerative colitis (UC) is common. Proctitis may affect the postoperative outcomes of ileal pouch-anal anastomosis (IPAA). This study aims to explore associations between rectal stump proctitis and short-term postoperative complications (POCs) after proctectomy and IPAA for UC. Methods This retrospective single-centre study included patients who underwent proctectomy, IPAA and protective ileostomy for UC from 2000-2023. Data were retrieved from our prospectively-maintained database. Exclusion criteria were dysplasia or cancer (103 pts), missing pathology results (50 pts), undetermined colitis or Crohn’s Disease features at proctectomy (18 pts). All patients underwent three-staged IPAA and were divided into four groups according to the rectal stump proctitis status at pathology: remission, mild, moderate, and severe proctitis. A stepwise binary logistic regression analysis was performed for each short-term outcome. Models included variables with a different distribution according to the outcome (p-value ≤0.1). Results We included 785 patients who underwent proctectomy and IPAA. At pathology, remission was achieved by 162 (20.6%) patients, while proctitis of the rectal stump was mild in 211 (26.9%), moderate in 246 (31.3%), and severe in 166 (21.1%) patients, respectively. Table 1 details population characteristics and outcomes according to the proctitis status. Patients with moderate and severe proctitis received more preoperative biologics and ongoing systemic steroids at surgery. While they underwent previous abdominal surgery less frequently, the laparoscopy rate was lower with a longer postoperative length of stay. At multivariate (Table 2), Medical POCs were independently associated with ongoing antibiotics (OR 2.29 [1.01-5.20] p=0.047) and ASA score≥3 (OR 1.93 [1.11-3.35] p=0.019). Surgical POCs were independently associated with ongoing systemic steroids (OR 2.09 [1.19-3.68] p=0.011, while ongoing antibiotics (OR 0.2 [0.04-0.86] p=0.031) and laparoscopy (OR 0.53 [0.28-1.00] p=0.049) were protective. Intra-abdominal septic complications (IASCs) and abdominal/pelvic abscesses were independently associated with the proctitis status (OR 1.1 [1.06-2] p=0.018 and OR 1.56 [1.08-2.25] p=0.017, respectively). Conclusion Rectal stump proctitis was independently associated with postoperative abdominal and pelvic abscesses and IASCs after proctectomy and IPAA for UC. The association between proctitis and IPAA’s long-term outcomes and pouch failure need to be further explored.