Adipocyte-derived adiponectin has an antiatherosclerotic effect that acts independently of its antidiabetic effect. Plasma adiponectin levels are generally low in subjects with coronary artery disease. In this study, the relationship between the plasma adiponectin level and the severity of coronary artery disease, as assessed using the Gensini score, an index for the severity of coronary artery stenosis, was investigated. The subjects of the study were 104 patients (72 men and 32 women; BMI, 23.5 ± 3.3 kg/m²; age, 63.6 ± 10.1 years) admitted to Tokyo University Hospital for coronary angiography. Plasma adiponectin levels were inversely correlated with the insulin resistance index HOMA-IR (P = 0.0127). The plasma adiponectin level was significantly associated with the Gensini score (P = 0.0332). After adjustment for conventional risk factors for cardiovascular diseases, the plasma adiponectin level tended to be inversely correlated with the Gensini score (P = 0.087). The measurement of plasma adiponectin levels may be useful for predicting the severity of coronary artery stenosis.