Circulating plasma adiponectin, an adipocyte-derived protein, has been shown to be decreased in obese subjects as well as in patients with type 2 diabetes and also in subjects who do not have diabetes, but are insulin resistant. We assessed the relationship between plasma levels of adiponectin, the metabolic syndrome and the occurrence of small dense LDL particles (pattern B) in 101 clinically healthy middle-aged subjects recruited from the general population. Low adiponectin levels were associated with the metabolic syndrome and low-density lipoprotein (LDL) particle size (r =.55, P <.001). The relationship between adiponectin and LDL particle size remained in a multiple regression model, in which adiponectin and total body fat explained 30% of the variability in LDL particle size. Furthermore, subjects in the lowest tertile of adiponectin had an increased risk of having pattern B (risk odds ratio [ROR] = 5.6). Because this was a cross-sectional study, no conclusions can be drawn about causality. This is the first population-based study in man demonstrating a relationship between small dense LDL particles and adiponectin.