Background Patients with risk factors or established atherosclerotic cardiovascular disease remain at high-risk for ischemic events. Triglyceride levels may play a causal role. Methods and Results We performed a retrospective study of adults aged ≥45 years receiving statin therapy, with a low-density lipoprotein cholesterol of 41 to 100 mg/dL, and ≥1 risk factor or established atherosclerotic cardiovascular disease between 2010 and 2017. Outcomes included death, all-cause hospitalization, and major adverse cardiovascular events (myocardial infarction, stroke, or peripheral artery disease). The study sample included 373 389 primary prevention patients and 97 832 secondary prevention patients. The primary prevention cohort had a mean age of 65±10 years, with 51% women and 44% people of color, whereas the secondary prevention cohort had a mean age of 71±11 years, with 37% women and 32% people of color. Median triglyceride levels for the primary and secondary prevention cohorts were 122 mg/dL (interquartile range, 88-172 mg/dL) and 116 mg/dL (interquartile range, 84-164 mg/dL), respectively. In multivariable analyses, primary prevention patients with triglyceride levels ≥150 mg/dL were at lower adjusted risk of death (hazard ratio [HR], 0.91; 95% CI, 0.89-0.94) and higher risk of major adverse cardiovascular events (HR, 1.14; 95% CI, 1.05-1.24). In the secondary prevention cohort, patients with triglyceride levels ≥150 mg/dL were at lower adjusted risk of death (HR, 0.95; 95% CI, 0.92-0.97) and higher risk of all-cause hospitalization (HR, 1.03; 95% CI, 1.01-1.05) and major adverse cardiovascular events (HR, 1.04; 95% CI, 1.05-1.24). Conclusions In a contemporary cohort receiving statin therapy, elevated triglyceride levels were associated with a greater risk of atherosclerotic cardiovascular disease events and lower risk of death.