We investigated the relationship between plasma adiponectin levels and the parameters of the metabolic syndrome among Koreans. In 67 male and 115 female subjects, aged from 30 to 70 years, plasma adiponectin levels were positively correlated with HDL-cholesterol levels (r = 0.295, P<0.001), but negatively correlated with waist circumference (r = -0.140, P = 0.020), triglycerides (r = -0.174, P = 0.021), fasting plasma glucose (r = -0.159, P = 0.036), fasting plasma insulin (r = -0.172, P = 0.023) and HOMA-IR (r = -0.182, P<0.001), after adjustment for age, sex, and BMI. Stepwise multiple regression analyses revealed that HDL-cholesterol, sex, and HOMA-IR were the independent associated factors for plasma adiponectin levels. Multiple logistic analyses demonstrated that HOMA-IR, BMI, and age were the predominant independent factors associated with the metabolic syndrome, while plasma adiponectin levels exhibited a protective effect against the presence of the metabolic syndrome according to both NCEP ATP III criteria and IDF definition. Hypoadiponectinemia is associated with the phenotype of the metabolic syndrome as well as components of the metabolic syndrome.