In 1998, the World Health Organization (WHO) accepted the diagnostic criteria proposed in 1997 by the American Diabetes Association (ADA) and confirmed that, independent of age, the fasting plasma glucose (FPG) level from and above 126mg/dl in the morning should be considered as diabetic, while subjects with FPG 110-125mg/dl have an impaired fasting glucose (IFG), compared with the normal fasting glucose (NFG) level (up to 110mg/dl). In a pool of 4492 elderly people (65-84 years), we assessed the significance and meaning of these new diagnostic criteria of diabetes. A 5-year follow-up was carried out, during which out of 4492 elderly subjects, 2750 were re-examined. As regards the diagnosis, we applied both the criteria of WHO (1985, 1998). At our first observation (1992), 13.1% were diabetic in the elderly group, if applying the WHO (1985) criteria, and 15.1% applying the ADA-WHO definitions. When re-analyzing the subjects with FPG of 126-139mg/dl after 5 years, it became evident that the diagnosis of diabetes is not stable in this group, because 50.7% of them displayed FPG<126mg/dl (14.5% IFG; 36.2% even NFG). It means that the significance of FPG and the conditions of diabetes are different in the elderly, as compared with the younger adults. Furthermore, the oral glucose tolerance test (OGTT) of 60 elderly subjects in the age range of 71-80 years, admitted in our day hospital, were considered. Among the subjects with an FPG 126-140mg/dl, the OGTT was of diabetic type in 90%, while among IFG and NFG subjects, it was in 50 and 10%, respectively. In conclusion, in elderly subjects with FPG of 126-140mg/dl, the diagnosis of diabetes is not stable and requires further confirmation.