In order to study the relationships of body fat distribution, insulin sensitivity and cardiovascular risk factors in lean, healthy non-diabetic Thai men and women, 32 healthy, non-diabetic subjects, 16 men and 16 women, with respective mean age 28.4+/-6.6 (S.D.) and 32.8+/-8.9 years, mean BMI 21.0+/-2.8 and 21.2+/-3.7 kg/m(2), were measured for total body fat and abdominal fat by dual energy X-ray absorptiometry (DEXA), anthropometry and insulin sensitivity by euglycemic hyperinsulinemic clamp. Cardiovascular risk factors included fasting and post-glucose challenge plasma glucose and insulin, blood pressure, lipid profile, fibrinogen and uric acid. For similar age and BMI, men had a lower amount and percent of total body fat, but had a higher proportion of abdominal/total body fat than women. In men, insulin sensitivity, as determined by glucose infusion rate during euglycemic hyperinsulinemic clamp, was inversely correlated with total body fat, abdominal fat, BMI and waist circumference, whereas only total body fat, but not abdominal fat, BW and hip circumference were inversely correlated with insulin sensitivity in women. No cardiovascular risk factors, except area under the curve (AUC), of plasma insulin in women correlated with insulin sensitivity when adjusted for total body fat. After age adjustment, total body fat was better correlated with fasting and AUC of plasma glucose and insulin in men and with systolic blood pressure as well as triglyceride levels in women. Only HDL-C in men was better correlated with abdominal fat. In conclusion, there were sex-differences in body fat distribution and its relationship with insulin sensitivity and cardiovascular risk factors in lean, healthy non-diabetic Thai subjects. Total body fat was a major determinant of insulin sensitivity in both men and women, abdominal fat may play a role in men only. Body fat, not insulin sensitivity, was associated with cardiovascular risk factors in these lean subjects.