To investigate the association of waist circumference with insulin resistance in obese young Japanese men.In this cross-sectional study, we evaluated 92 obese young Japanese men (age: 18–29 years; mean BMI±SD: 33±3kg/m 2 ) for anthropometric and metabolic parameters and the homeostasis model assessment of insulin resistance (Homa-IR).Waist circumference ranged from 87.5cm to 129cm. Subjects with waist circumferences in the top quartile had higher insulin (Ln-transformed) and Homa-IR (Ln-transformed) compared with those in the bottom quartile. Fasting blood glucose and HbA1c were lower among subjects in the second-lowest quartile but not the second-highest quartile or the top quartile compared with those in the bottom quartile.Insulin resistance is associated with waist circumference in moderately to highly obese young Japanese men. Suppression of blood glucose by enhanced insulin secretion triggered by the increase of insulin resistance may begin to lose its effect as waist circumference becomes larger.