Aims/hypothesis. To study the risk of women with impaired fasting glucose (IFG) as against impaired glucose tolerance (IGT) developing diabetes.¶Methods. Oral glucose tolerance tests (75 g) were done in 265 women selected at random at baseline (age 55–57 years) and at a 10-year follow-up. Of the women 42 had IFG/NGT (fasting glucose 6.1–6.9 mmol/l, 2-h glucose < 7.8 mmol/l), 66 IGT/NFG (2-h glucose 7.8–11.0 mmol/l, fasting glucose < 6.1 mmol/l), 30 IGT/IFG and 127 NFG/NGT.¶Results. The 10-year progression to diabetes was similar in IGT/NFG (12.1 %) and IFG/NGT groups (11.9 %, p = 0.97). In IGT/IFG, 20.0 % had developed diabetes, which was not significantly higher than in IFG/NGT and IGT/NFG (p = 0.53). In NFG/NGT at baseline, only 3.9 % had developed diabetes, which was lower than in the other groups (p = 0.023).¶Conclusion/interpretation. Fasting and 2-h glucose concentrations are equally good in predicting diabetes development over a 10-year period in Caucasian postmenopausal women. Because IGT is more common than IFG, measuring only fasting glucose concentrations would, however, result in missing a prediabetic stage in a large group of people at risk for diabetes and cardiovascular diseases. [Diabetologia (2000) 43: 1224–1228]