AIM To investigate the clinical course of ulcerative colitis(UC)patients who develop acute pancreatitis.METHODS We analyzed 3307 UC patients from the inflammatory bowel disease registry at Asan Medical Center from June 1989 to May 2015.The clinical course of UC patients who developed acute pancreatitis was compared with that of non-pancreatitis UC patients.RESULTS Among 51 patients who developed acute pancreatitis,13(0.40%)had autoimmune,10(0.30%)had aminosalicylate-induced,and 13(1.73%)had thiopurineinduced pancreatitis.All 13 patients with autoimmune pancreatitis(AIP)had type 2 AIP.Two(15.4%)patients had pre-existing AIP,and three(23.1%)patients developed AIP and UC simultaneously.Compared to non-pancreatitis patients,AIP patients had UC diagnosed at a significantly younger age(median,22.9 years vs 36.4 years;P=0.001).AIP and aminosalicylate-induced pancreatitis patients had more extensive UC compared to non-pancreatitis patients.All patients with pancreatitis recovered uneventfully,and there were no recurrences.Biologics were used more frequently in aminosalicylate-and thiopurine-induced pancreatitis patients compared to non-pancreatitis patients[adjusted OR(95%CI),5.16(1.42-18.67)and6.90(1.83-25.98),respectively].Biologic utilization rate was similar among AIP and non-pancreatitis patients[OR(95%CI),0.84(0.11-6.66)].Colectomy rates for autoimmune,aminosalicylate-induced,and thiopurineinduced pancreatitis,and for non-pancreatitis patients were 15.4%(2/13),20%(2/10),15.4%(2/13),and7.3%(239/3256),respectively;the rates were not significantly different after adjusting for baseline disease extent.CONCLUSION Pancreatitis patients show a non-significant increase in colectomy,after adjusting for baseline disease extent. AIM To investigate the clinical course of ulcerative colitis (UC) patients who develop acute pancreatitis. METHODS We analyzed 3307 UC patients from the inflammatory bowel disease registry at Asan Medical Center from June 1989 to May 2015. The clinical course of UC patients who have acute pancreatitis was compared with that of non-pancreatitis UC patients .RESULTS Among 51 patients who developed acute pancreatitis, 13 (0.40%) had autoimmune, 10 (0.30%) had aminosalicylate-induced, and 13 (1.73%) had thiopurineinduced pancreatitis. All 13 patients with autoimmune pancreatitis (AIP) had type 2 AIP.Two (15.4%) patients had pre-existing AIP, and three (23.1%) patients developed AIP and UC simultaneously. Computed to non-pancreatitis patients, AIP patients had UC diagnosed at a significant younger age (median, 22.9 years vs 36.4 years; P = 0.001) .AIP and aminosalicylate-induced pancreatitis patients had more extensive UC compared to non-pancreatitis patients. All patients with pancreatitis recovered uneventfully, and there are no recurrences.Biologics were used more frequently in aminosalicylate-and thiopurine-induced pancreatitis patients compared to non-pancreatitis patients [adjusted OR (95% CI), 5.16 (1.42-18.67) and 6.90 (1.83-25.98), respectively]. Biologic utilization rate was similar among AIP and non-pancreatitis patients [OR (95% CI), 0.84 (0.11-6.66)]. Colectomy rates for autoimmune, aminosalicylate-induced, and thiopurineinduced pancreatitis, and for non-pancreatitis patients were 15.4% (2/13), 20% (2/10), 15.4% (2/13), and 7.3% (239/3256), respectively; the rates were not significantly different after adjusting for baseline disease extent. CONCLUSION Pancreatitis patients show a non-significant increase in colectomy, after adjusting for baseline disease extent.