Traditional cardiac risk factors only partially explain the biological mechanisms by which persons of lower socioeconomic status (SES) have higher cardiovascular risk. Dietary factors, resulting in lower circulating levels of (n-3) fatty acids, may also contribute to the increased risk of cardiovascular disease (CVD) in patients with low SES. We tested whether low SES is associated with RBC levels of (n-3) fatty acids in patients with coronary heart disease. We performed a cross-sectional analysis of 987 adults with stable coronary artery disease (CAD) recruited from San Francisco area outpatient clinics. Four SES measures (household income, education, occupation, and housing status) were assessed by self-report. RBC fatty acid levels of 2 (n-3) fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), were measured in venous blood samples from fasting subjects. Participants with lower household income, education, occupation, and housing status had lower RBC levels of (n-3) fatty acids (P < 0.001 for all 4 measures). In multivariable models, household income, education, and occupation remained strongly associated with DHA and EPA levels after adjustment for demographic factors, BMI, physical activity, statin use, and kidney function (P < 0.001 for all 3 measures). Housing status was not associated with DHA or EPA after multivariable adjustment. Among patients with CAD, 3 indicators of low SES, household income, education, and occupation, were strongly associated with lower RBC levels of (n-3) fatty acids. Our results raise the possibility that (n-3) fatty acids may be an important mediating factor in the association between low SES and CVD.