['Sleep apnea has been implicated as an independent risk factor for atherosclerotic coronary artery disease (CAD). An association between the severity of sleep apnea and total cholesterol levels has previously been reported. However, the association with small dense low density lipoprotein (LDL) cholesterol concentration (subclass B), one of the strongest predictors of atherosclerosis, is unknown. We examined the relationship between sleep apnea and LDL subclass B, considering body size.', 'This is a cross-sectional observational cohort of participants enrolled in a cardiovascular health study. Sleep apnea was assessed with a validated portable monitor. Lipid panels included total cholesterol, triglycerides, high density lipoprotein cholesterol, LDL cholesterol, and LDL subclasses A, B, and A/B. Sleep apnea was analyzed categorically using the apnea hypopnea index (AHI).', 'A total of 519 participants were evaluated. Mean age was 58.7 ± 7.4 years; BMI was 29.6 ± 5.7; 65% were female; 59% were Caucasian, and 37% were African American. Among participants with abnormal waist circumference by ATP III criteria, moderate to severe sleep apnea (AHI ≥ 25) was not independently associated with LDL subclass B. In contrast, among participants with normal waist circumference, moderate to severe sleep apnea was associated with 4.5-fold odds of having LDL subclass B.'] Is sleep apnea related to the atherogenic phenotype , lipoprotein subclass B?