Little information is available regarding how body fatness and cardio/respiratory fitness (CRF) are associated with serum vaspin. The purpose of the study was to investigate the combined effect of body mass index (BMI) and CRF on serum vaspin in Korean young men. In a cross-sectional study, we examined 490 Korean young men (mean age 23.8 +/- 2.5 years) who were voluntarily recruited. Body fatness and fasting levels of serum insulin, adiponectin, and vaspin were measured. CRF was quantified as the minute volume of oxygen consumption (VO(2)) measured during a graded treadmill test. We assigned individuals to either low or middle or high third CRF tertiles based on age-adjusted VO(2max). We also assigned individuals to either a lean weight (LN) or obese (OB) group based on body fatness levels, in which a BMI value >/=25 kg/m(2) was used as an indicator of Pacific-Asian obesity. Group analyses showed significant interaction effects between fatness and CRF on fasting insulin and serum vaspin such that the OB group with low CRF levels had significantly higher insulin and vaspin concentrations than the OB counterparts with moderate to high CRF levels, and no such CRF-based sub-group differences in insulin and vaspin were found in the LN groups. Regression analyses show that BMI, waist circumference, VO(2), and fasting insulin explain approximately 18% of the individual variations in serum vaspin concentration in this study population. This is the first study to show that high body fatness along with low CRF might contribute to increased vaspin concentrations in Korean young men.