This population based study was undertaken to ascertain the overall prevalence of diabetes mellitus (DM) and impaired glucose tolerance (IGT) in the elderly using the WHO criteria. The role of obesity in the development of DM or IGT has been investigated for both sexes per decade of age. Furthermore the potential for DM to increase with age, as has been suggested before, has been evaluated using the IGT as a proportion of total glucose intolerance (IGT/TGI) for the same parts of the tested sample. From the 647 persons registered as elderly people in a small town in northern Greece (total population 5875 people), 66 persons did not participate in this survey. Fifty-six subjects (9.7%) had previously diagnosed DM. The remainder were tested using fasting blood glucose measurements or an oral glucose tolerance test (OGTT). The prevalence of previously undiagnosed DM according to fasting blood glucose values or after 2 h of 75 g load values was 10.1% and 9.3%, respectively. Thus the overall prevalence of DM was 29.1% and of IGT was 15.1%. These data support an increased frequency of DM (65% previously undiagnosed) and IGT in the elderly, whereas this population's susceptibility seems to decline in the older groups for both sexes. Obesity remains a risk factor for DM and IGT particularly among the younger groups although its role has been found to decline with age.