BACKGROUND: Ileorectal anastomosis in patients with ulcerative colitis results in decreased postoperative morbidity and better functional outcome but leads to increased risk for rectal cancer compared with IPAA. OBJECTIVE: This study aims to compare ileorectal anastomosis with IPAA in ulcerative colitis by using a decision model. DESIGN: A Markov simulation model was designed to simulate clinical events of ileorectal anastomosis and IPAA over a time horizon of 40 years with time cycles of 1 year. All probabilities and utilities were derived from observational studies, identified after a systematic literature search using MEDLINE. Primary outcomes were life-years and quality-adjusted life-years. Deterministic and probabilistic sensitivity analyses were performed. SETTINGS: A decision model using Markov simulation was designed. PATIENTS: The base case was a 35-year-old patient with ulcerative colitis and a relatively preserved rectum. MAIN OUTCOMES MEASURES: The primary outcome measures were (quality-adjusted) life-years. RESULTS: The model resulted in lower life-years (36.22 vs 37.02) and higher quality-adjusted life-years (33.42 vs 31.57) for ileorectal anastomosis. This was confirmed after probabilistic sensitivity analysis. The model was sensitive to the utility of ileorectal anastomosis, IPAA, and end-ileostomy. A higher proportion of patients with ileorectal anastomosis will develop rectal cancer (7.6% vs 3.2%) and 43.5% of all patients with ileorectal anastomosis will end with an ileostomy as opposed to 23.0% of all patients with IPAA. LIMITATIONS: The study was limited by characteristics inherent to modeling studies, including assumptions necessary to build the model, data input based on best available but often limited evidence, and unavoidable extra- and interpolation of data. CONCLUSIONS: Ileorectal anastomosis was the preferred treatment option when quality-adjusted life-years were the outcome, with higher life-years for IPAA. This model highlights that both surgical strategies are useful in patients who have ulcerative colitis with a relatively spared rectum. See Video Abstract at http://links.lww.com/DCR/B249.