The general requirements for establishing diagnostic criteria with tests of glucose tolerance are discussed in relation to standards for gestational diabetes that are in current use. Data are presented to show that even when remissions of gestational diabetes occur with the progression of pregnancy, the risk of subsequent diabetes remains unaltered. The prognostic potential that fasting blood glucose levels has for the outcome of pregnancy is also considered. Finally the dependence of prevalence rates for gestational diabetes on the criteria selected and their substantial effect on assessment of screening methods is demonstrated.