Objective To evaluate the present Chinese body mass index(BMI) criteria with body fat percentage(BF%) in determining obesity in Chinese population.Methods A total of 4 907 subjects(age:20-90 yrs) were enrolled in the baseline survey of a longitudinal epidemiological study,and 2 638 of them were reevaluated in 5.5 years later.The Chinese BMI and WHO BF%were used to define obesity,respectively.Results The diagnostic agreement between the Chinese BMI and WHO BF%definitions for obesity was poor for both men(kappa:0.210,95%CI:0.179-0.241) and women(kappa:0.327, 95%CI:0.296-0.358).However,BMI had a good correlation with BF%both in men(r:0.785,P<0,01) and women(r:0.864, P<0.01).The age and sex-adjusted relative risks(RR) for incidence of type 2 diabetes(T2DM) were significantly higher in subjects with intermediate BF%(BF%:20.1%-25%for men,30.1%-35%for women)(RR:2.35,95%CI:1.23-4.48) and high BF%(BF%>25%for men and>35%for women)(RR:2.89,95%CI:1.43-5.81),or in subjects with high BMI(BMI≥28 kg/m~2)(RR:2.46,95%CI:1.31-4.63) when compared to those with low BF%(BF%≤20%for men and≤30%for women) or low BMI(BMI<24 kg/m~2) respectively.No difference in risk could be found in those with intermediate BMI(BMI:24-27.9 kg/m~2)(RR:1.44,95%CI:0.86-2.40),as compared to those with low BMI(BMI<24 kg/m~2),whose BF%ranged widely from 7.8 to 50.3%.Conclusion BMI was correlated with BF%.Both BMI and BF%were associated with high risk for T2DM. However,BMI had its limitations in the interpretation of subjects with BMI between 24 and 27.9 kg/m~2. Objective To evaluate the present Chinese body mass index (BMI) criteria with body fat percentage (BF%) in determining obesity in Chinese population. Methods A total of 4 907 subjects (age: 20-90 yrs) were enrolled in the baseline survey of a longitudinal epidemiological study, and 2 638 of them were reevaluated in 5.5 years later. The Chinese BMI and WHO BF% were used to define obesity, respectively. Results The diagnostic agreement between the Chinese BMI and WHO BF% definitions for obesity was poor for Both men (kappa: 0.210, 95% CI: 0.179-0.241) and women (kappa: 0.327, 95% CI: 0.296-0.358) Were significantly higher in subjects with intermediate BF% (BF%: < 20.1% -25% for men, 30.1% -35% for women) (RR: 2.35, 95% CI: 1.23-4.48) and high BF% (BF%> 25% for men and> 35% for women) : 2.89, 95% CI: 1.43-5.81), or in subjects with high BMI (BMI> 28 kg /m~2)(RR:2.46,95%CI:1.31-4.63) when compared to those with low BF% (BF% ≤20% for men and ≤30% for women) or low BMI (BMI <24 kg / m 2) respectively. Difference in risk could be found in those with intermediate BMI (BMI: 24-27.9 kg / m 2) (RR: 1.44, 95% CI: 0.86-2.40), as compared to those with low BMI (BMI <24 kg / m 2), whose BF% ranged widely from 7.8 to 50.3% .Conclusion BMI was correlated with BF% .Both BMI and BF% were associated with high risk for T2DM. However, BMI had its limitations in the interpretation of subjects with BMI between 24 and 27.9 kg / m ~ 2.