Background: There is a paucity of contemporary data estimating the incidence of major adverse cardiovascular events (MACE) in patients with established atherosclerotic disease or multiple risk factors managed in routine practice. We estimated 1- and 4-year incidences of MACE and the association between MACE and vascular beds affected in these patients. Methods and Results: Using US IBM MarketScan data from January 1, 2013 to December 31, 2017, we identified patients ≥45 years old with established coronary artery disease, cerebrovascular disease, peripheral artery disease, or the presence of ≥3 risk factors for atherosclerosis during 2013 with a minimum of 4 years of follow-up. We calculated 1- and 4-year incidences of MACE (cardiovascular death or hospitalization for myocardial infarction or ischemic stroke). A Cox proportional hazards regression model adjusted for age and sex was used to evaluate the association between vascular bed number/location(s) affected and MACE. We identified 1 302 856 patients with established atherosclerotic disease or risk factors for atherosclerosis. Coronary artery disease was present in 16.9% of patients, cerebrovascular disease in 7.6%, peripheral artery disease in 13.6%, and risk factors for atherosclerosis only in 66.0%. The 1- and 4-year incidences of MACE were 1.4% and 6.9%, respectively. At 4 years, MACE was more frequent in patients with atherosclerotic disease in a single (hazard ratio=1.51, 95% CI=1.48–1.55), 2-(hazard ratio=2.35, 95% CI=2.27–2.44), or all 3 vascular beds (hazard ratio=3.30, 95% CI=2.97–3.68) compared with having risk factors for atherosclerosis. Conclusions: Patients with established atherosclerotic disease or who have multiple risk factors and are treated in contemporary, routine practice carry a substantial risk for MACE at 1- and 4- years of follow-up. MACE risk was shown to vary based on the number and location of vascular beds involved.