In a 10-yr prospective population study 406 subjects who were 70 yr old received an oral glucose tolerance test. Of these subjects 169 were retested at 80. Three sets of diagnostic criteria were evaluated, of which the WHO criteria are recommended for screening studies in this age group. The prevalences of diabetes mellitus (DM) and impaired glucose tolerance (IGT) according to the latter criteria were 10% vand 26% at 70 and 12% and 35% at 80 in men and women. Excess 10-yr mortality was seen in both sexes when DM existed at 70, and in men also when IGT existed at this age. The excess mortality in men could solely—and in women partly—be explained by cardiovascular diseases. The 10-yr incidence of DM was 20% if IGT existed at 70, but only 4% when normal glucose tolerance was present at 70.