Although gestational diabetes is estimated to complicate between 1% and 5% of pregnancies, there are only limited data on the role of race/ethnicity as well as other risk factors in the development of this disorder. Epidemiologic characteristics of gestational diabetes were assessed in an ethnically diverse cohort of 10,187 women who had undergone standardized screening for glucose intolerance and who delivered a singleton infant at the Mount Sinai Medical Center in New York City between January 1987 and December 1989. The overall prevalence of gestational diabetes was 3.2%. Multiple logistic regression analysis showed excess risks for Oriental women, Hispanics born in Puerto Rico or elsewhere outside the United States, women from the Indian subcontinent and the Middle East, older mothers, heavier women, those with a positive family history of diabetes, women with a history of infertility, and those who delivered on the clinic service. These data suggest that, after controlling for traditional risk factors (maternal age, prepregnancy weight, and a family history of diabetes), Orientals, first generation Hispanics, women from the Indian subcontinent and the Middle East, those with a history of infertility, and low socioeconomic status women are at an increased risk for gestational diabetes.