Obesity and weight increase during adult life are strong predictors of type 2 diabetes. Whether fasting plasma glucose (FPG) is likewise related to body weight as well as with its increase during the adult life in obese-overweight people and whether this relationship is different between the genders is the question asked by the present study. We measured FPG in 1063 overweight-obese subjects (395M/668F) with BMI > or =25 kgm(-2) and classified with no history of diabetes and with a FPG< 7 mmol/l, who consequently came to the Outpatient Clinic of our Diabetes Unit to obtain dietetic advice. Weight increase was determined as the difference between actual weight and weight at 18 years (weight-diff), including only patients with weight-diff> 0. By univariate analysis age, BMI, waist circumference and weight change were loosely related to FPG in both sexes, even if the relation between plasma glucose and anthropometric variables was more consistent in females. By multivariate regression analysis, after adjusting for age, waist circumference, menopausal status and smoking habit, FPG was significantly related to both waist circumference and weight-diff only in women. Odds Ratio for fasting hyperglycaemia (FPG> 6.11 mmol/l), for each S.D. unit increase in weight-diff, after adjusting for age, waist circumference, smoking habit and menopausal status was 1.272; 95% CI: 0.863-1.901 (p=ns) for males and 1.800; 95% CI: 1.239-2.652 (p=0.002) for women. In conclusion our findings suggest that in non-diabetic overweight-obese people, after controlling for main cofounders, anthropometric variables and in particular waist circumference and weight change after 18 years are linearly related to FPG in women, independently predicting the risk of fasting hyperglycaemia only in these latter.