Background: Inflammation is a mediator of atherosclerosis progression. However, it remains unclear whether immunoglobulin G4 (IgG4)-related immuno-inflammation may play a specific role in cardiovascular disease. Methods: We used a case-cohort design to analyze the association of serum IgG4 levels with future cardiovascular events. The sample included 561 cases of the primary end point, defined as cardiovascular death, myocardial infarction, ischemic stroke, or unstable angina, and a random subcohort of 1688 (1409 males; mean age, 68.1 ± 8.4 years), of whom 73 were also cases, selected from 12413 eligible participants with stable coronary artery disease in the Randomized Evaluation of Aggressive or Moderate Lipid Lowering Therapy with Pitavastatin in Coronary Artery Disease (REAL-CAD) study. Results: This case-cohort study had a median follow-up of 3.9 years (interquartile range [IR] 2.9-4.6). Serum IgG4 levels at baseline were 45.3 mg/dL (IR 37.9-58.9), and 845 (50%) took high-dose statins in the subcohort sample. In Cox regression using age, gender, statin dose, high-sensitivity C-reactive protein (hsCRP), body mass index, estimated glomerular filtration rate (eGFR), hypertension, diabetes, and serum lipid profiles, including low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides, as covariates, the highest IgG4 quartile was predictive of the primary end point at 4 years (hazard ratio [HR] 1.44, 95% confidence interval [CI] 1.03-2.00, P=0.031), compared with the lowest quartile. Similar results were observed for the secondary end point, a composite of the primary end point plus coronary revascularization (HR 1.60, 95% CI 1.16-2.20, P=0.004). Conclusions: Elevated serum IgG4 level at baseline predicted long-term cardiovascular outcomes independent of established risk factors and high-dose statin therapy in patients with stable CAD. Serum IgG4 may reflect residual cardiovascular risk.