Prevalence of Colorectal Neoplasms and Mortality in New Users of Low-Dose Aspirin With Lower Gastrointestinal Bleeding Background: Aspirin inhibits platelet function and may therefore accelerate early lower gastrointestinal bleeding (LGIB) from colorectal cancer (CRC) precursor polyps. The bleeding may increase endoscopic polyp detection. Study Question: To estimate the prevalence of polyps and CRC comparing new users of low-dose aspirin with nonusers who all received a diagnosis of LGIB and to investigate the mortality among these patients. Study Design: Using Danish nationwide health registries, we conducted a cohort study (2006–2013) of all new aspirin users who also received a diagnosis of LGIB (n = 40,578). Each new user was matched with 5 nonusers with LGIB by gender and age at the LGIB diagnosis date. Measures and Outcomes: We computed the prevalence and prevalence ratios (PRs) of colorectal polyps and CRCs, and the mortality ratios within 6 months after the LGIB, comparing new users with nonusers. Results: We identified 1038 new aspirin users and 5190 nonusers with LGIB. We observed 220 new users and 950 nonusers recorded with endoscopically detected polyps. New aspirin users had a higher prevalence of conventional {PR = 1.28 [95% confidence interval (CI): 1.06–1.55]} and serrated [PR = 1.31 (95% CI: 0.95–1.80)] polyps. New users and nonusers had a similar prevalence of CRC [PR = 1.04 (95% CI: 0.77–1.39)]. However, after stratifying by location of CRC, the prevalence of proximal tumors was lower [PR = 0.71 (95% CI: 0.35–1.43)] in new users than in nonusers. No difference in mortality was observed. Conclusions: These findings indicate that new use of low-dose aspirin is associated with an increased detection of colorectal polyps compared with nonuse. Address for correspondence: Department of Clinical Epidemiology, Aarhus University Hospital, Olof Palmes Allé 43-45, Aarhus 8200, Denmark. E-mail: frtroe@clin.au.dk The Department of Clinical Epidemiology, Aarhus University Hospital, receives funding for other studies from companies in the form of research grants to (and administered by) the University of Aarhus. None of these studies have relation to the present paper. The authors have no conflicts of interest to declare. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (www.americantherapeutics.com). Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.