Background: Colorectal neoplasm, including colorectal adenoma, is associated with old age, cigarette smoking, and the presence of metabolic syndromes. These are also risk factors for cardiovascular disease. Carotid ultrasonography is a noninvasive test that can predict the risk of cardiovascular disease and may be another test that may provide indications of these risk factors. This study aimed to investigate the association between colorectal adenomatous polyps and carotid atherosclerosis. Methods: This study included 548 adults who underwent colonoscopy and carotid ultrasonography for a health examination between March 2013 and December 2017 at a university hospital in South Korea. Abnormal carotid sonography findings included either increased carotid intima-media thickness or presence of carotid plaques. Results: The proportion of subjects with overall colorectal adenomatous polyps was 31.0% (170/548). Colorectal adenoma was more prevalent in the presence of abnormal carotid ultrasonography findings (38.6% vs. 27.6%, p = 0.013). Colorectal adenomatous polyp was significantly associated with abnormal carotid ultrasonography findings (OR = 1.65; 95% CI, 1.12–2.42, p = 0.011) in a multivariate analysis after adjusting for age, sex, cigarette smoking, alcohol consumption, and presence of metabolic syndrome. Conclusion: Colorectal adenoma is significantly associated with carotid atherosclerosis.