Gestational diabetes is associated with an increased risk of fetal macrosomia and perinatal death. Immigrant mothers from Vietnam who delivered in the Mercy Hospital for Women between January 1, 1979 and December 31, 1990 were investigated to assess their risk of gestational diabetes, the factors that were associated with gestational diabetes, and the prevalence of diabetes mellitus on follow-up. These mothers were compared with Australian-born mothers attending the same hospital and who delivered in the same period. Using a logistic regression model, gestational diabetes was found to be more common in Vietnam-born mothers who were older, who were primigravidas, or were underweight and the risk of gestational diabetes increased over the time period of the study. The adjusted relative risk of gestational diabetes for Vietnam-born women was 1.43 (95% confidence limits 1.10, 1.86) compared with Australian-born women. The incidence of gestational diabetes was 7.8% (144 of 1,839) in Vietnam-born mothers and 4.3% (1,173 of 27,086) in Australian-born mothers. Vietnam-born mothers also had a greater risk of diabetes mellitus on follow-up; 25% (17 of 68) of those with follow-up testing had developed diabetes mellitus within 9 years of diagnosis of gestational diabetes, in comparison with an incidence of 9% (52 of 581) of Australian-born mothers with follow-up testing. Vietnam-born mothers should have glucose tolerance testing performed during pregnancy to detect gestational diabetes and those diagnosed should have long-term follow-up to detect the development of diabetes mellitus.