Data from case-control and cross-sectional studies uniformly demonstrate an association between small, dense low-density lipoprotein and risk of coronary heart disease. This relationship may be attributable to the association of small, dense low-density lipoprotein with other atherogenic lipoproteins, the presence of the insulin resistance syndrome in subjects with small low-density lipoprotein, and/or the increased oxidative susceptibility of small, dense low-density lipoprotein particles. Furthermore, because small low-density lipoprotein appears to be a common trait in the general population, more than one of these atherogenic mechanisms may be operating simultaneously to increase risk of coronary heart disease.