GOALS:: To determine the prevalence of ulcerative colitis (UC) in autoimmune pancreatitis (AIP) patients in a tertiary referral hospital and to compare the clinical and pathologic characteristics and outcomes of UC associated with AIP (AIP-UC) and UC patients. BACKGROUND:: Recently, it was suggested that UC is associated with AIP. However, the prevalence of UC in AIP, together with the clinical characteristics and outcomes of AIP-UC are not clear. STUDY:: We retrospectively reviewed the medical records of AIP patients diagnosed at the Asan Medical Center. RESULTS:: Of the 104 patients with AIP, 6 (5.8%) were also diagnosed with UC. Serum immunoglobulin G (IgG) and IgG4 were elevated in 1 patient (16.7%), respectively, and 4 (66.7%) showed idiopathic duct-centric pancreatitis (type 2 AIP). Compared with 24 matched patients with UC only, AIP-UC patients had a lower body mass index (P=0.003), higher C-reactive protein levels (P=0.048), and higher Mayo scores (P=0.006) at diagnosis of UC. Two AIP-UC patients (33.3%), but none with UC only showed increased infiltration of IgG4-positive cells into the colonic tissues (P=0.006). During follow-up, 2 AIP-UC patients (33.3%) underwent colectomy and 1 (16.7%) died, but no colectomies or deaths occurred in the UC only group. CONCLUSIONS:: AIP patients seem to have a higher risk of UC compared with the general population. The increased IgG4-positive cellular infiltration in the colonic tissue suggests that UC may be an extrapancreatic manifestation of AIP.