Little information exists on the association between maternal country of birth and risk of gestational diabetes (GDM). We examined within each race-ethnicity group whether the risk of GDM differs between women born inside and outside the US. The study was a cohort study of 216 089 women who delivered an infant between 1995 and 2004 with plasma glucose data from the screening 50-g glucose challenge test and the diagnostic 100-g, 3-h oral glucose tolerance test. The age-adjusted prevalence of GDM varied by race-ethnicity and was lowest for non-Hispanic white (4.1%) and highest among Asian Indians (11.1%). In multivariable models, being born outside of the US was associated with an increased risk of GDM among black, Asian Indian, Filipina, Pacific Islanders, Chinese, Mexicans and non-Hispanic white women, whereas, Japanese and Korean foreign-born women had a decreased risk of GDM. Clinicians should be aware that among certain race-ethnicity groups women born outside the US may be at increased risk of GDM and may warrant special preventive and culturally sensitive care.