Adipokines play crucial roles in obesity-related insulin resistance in adults, but little is known in the general adolescent population. This study was designed to investigate the relationships between adipokines and metabolic parameters, the insulin resistance index, and proinflammatory cytokines in the general population of Japanese male adolescents. We studied 662 Japanese male high school students aged 16 to 17 years and 282 healthy Japanese male adults aged 30 to 61 years who received annual health checkups. High-molecular weight (HMW) adiponectin levels were significantly lower in adolescents (4.18 +/- 2.24 microg/mL) than in adults (4.84 +/- 3.20 microg/mL), despite body mass index (BMI) being significantly lower in adolescents. The HMW adiponectin levels correlated negatively with BMI and the homeostasis model assessment of insulin resistance index (HOMA-IR) in adults. In adolescents, HMW adiponectin correlated negatively with BMI and waist circumference, but not with HOMA-IR or other metabolic parameters except high-density lipoprotein cholesterol. Leptin levels correlated positively with HOMA-IR, triglycerides, tumor necrosis factor alpha, interleukin 6, and monocyte chemoattractant protein 1 and negatively with high-density lipoprotein cholesterol even after adjustment for BMI. These findings suggest that serum leptin is a more useful biomarker of fat accumulation-related insulin resistance, inflammation, and metabolic abnormalities than HMW adiponectin in the general population of male adolescents. The inverse correlation between adiponectin and insulin resistance may manifest in the later phase of obesity development.