AbstractObjective: We sought to establish reference values for a new direct assay for small dense LDL cholesterol (sdLDL-C) and to measure sdLDL-C concentrations in patients with established coronary heart disease (CHD) vs controls.Methods: Direct LDL-C and sdLDL-C were measured in samples from 3188 male and female participants of the Framingham Offspring Study, including 173 men and 74 women with CHD.Results: Postmenopausal status and male sex were associated with higher sdLDL-C concentrations (P < 0.0001). Cholesterol-lowering medication use was more frequent (P < 0.0001) in CHD patients than in controls (46.8% vs 11.4% in men; 35.1% vs 8.8% in women). In men, mean LDL-C was lower in CHD than in controls (3.22 vs 3.51 mmol/L, P < 0.0001), whereas mean sdLDL-C concentrations were similar (0.83 vs 0.84 mmol/L, P = 0.609). In women, mean LDL-C was similar in CHD and controls (3.53 vs 3.46 mmol/L, P = 0.543), but mean sdLDL-C was higher (0.83 vs 0.68 mmol/L, P = 0.0015). The mean percentage of LDL-C as sdLDL-C was higher in both men and women with CHD than controls (P < 0.01). Increased LDL-C and sdLDL-C were found in 10.4% and 22.0% of men and in 24.3% and 27.8% of women with CHD, respectively.Conclusions: Despite 4-fold greater cholesterol-lowering therapy use, CHD patients had mean LDL-C concentrations above the LDL-C goal of <2.6 mmol/L (<100 mg/dL). Although women with CHD had higher sdLDL-C concentrations than controls, this difference was not seen in men. These findings may explain some of the high residual risk of future CHD events in CHD patients.