Background/Aims: The U.S. Preventive Services Task Force (USPSTF) currently recommends aspirin for primary prevention of coronary heart disease in men 45.79 years old and strokes in women 55.79 years old when the potential cardiovascular disease benefit outweighs the potential harm of gastrointestinal hemorrhage. The complexity and time required to assess risks and benefits for primary prevention can be a barrier for providers to giving patients USPSTF-consistent recommendations, resulting in potential overuse and underuse. Methods: As part of a National Institutes of Health-funded randomized trial to lower cardiovascular risk, we developed a sophisticated web-based electronic health record (EHR)-integrated tool to guide aspirin recommendations as determined by algorithms assessing USPSTF criteria and major bleeding risks. Baseline data was collected for whether aspirin was algorithmically indicated (or not) for all patients at their first eligible primary care encounter in 20 clinics over 18 months. The analysis included patients age 18.75 (mean 58.4) with elevated cardiovascular disease risk (mean 10-year ASCVD risk 24.7%) and excluded patients with congenital heart defects or diabetes. Aspirin overuse and underuse was determined by comparing concordance with: a) the algorithmfs aspirin recommendation, and b) EHR-medication documentation of aspirin. Results: Of the 11,682 patients meeting eligibility criteria at baseline, aspirin was indicated in 8,722 (74.7%) and not indicated in 2,960 (25.3%). Among patients with an aspirin indication, 6,493/8,722 (74.4%) did not have aspirin documented (underuse). Among patients without an aspirin indication, 1,021/2,960 (34.4%) had aspirin documented (overuse). Conclusion: Overall, 7,514/11,682 (64.3%) of patients who met study inclusion criteria for age and cardiovascular risk exhibited either potential overuse or underuse of aspirin for primary cardiovascular disease prevention. Despite expected missing documentation of aspirin due to its over-the-counter availability, which would result in measures of greater underuse and lower overuse than actuality, it is clear that patient aspirin use is very commonly inconsistent with USPSTF guidelines. The recommendation to consider colorectal benefits in the latest USPSTF draft could make decisions about aspirin appropriateness even more complex. EHR-based tools to help providers assess individualized risks and benefits of aspirin could greatly improve the quality of aspirin recommendations and potentially reduce costly cardiovascular disease events while simultaneously reducing rates of aspirin-related hazards.