Recent studies show adverse outcomes of pregnancy among immigrant women from countries with high diabetes rates. We compared maternal and fetal outcomes in immigrant and Italian women with gestational diabetes mellitus (GDM) followed up at our center. Maternal characteristics considered were age, pre-pregnancy body mass index (BMI), HbA1c, frequency of insulin treatment, timing and mode of delivery, and hypertensive disorders; and, for fetal outcome, infants large or small for gestational age, and fetal complications. Pre-pregnancy BMI and HbA1c were higher in immigrant GDM women than in Italians, and more of them were on insulin. No differences in maternal outcome emerged between the two groups. More large for gestational age (LGA) babies were born to immigrant women than to Italians, but no other differences emerged. Apart from newborn LGA, maternal and fetal outcomes were comparable in our immigrant and Italian GDM women. Immigrant GDM women have favourable outcomes if given access to health care and language and cultural barriers are removed.