Objective: To compare perinatal outcomes between self-identified Hispanic and non-Hispanic white women with mild gestational diabetes mellitus (GDM) or glucose intolerance. Methods: In a secondary analysis of a mild GDM treatment trial, we compared perinatal outcomes by race and ethnicity for 767 women with glucose intolerance (abnormal 50-g 1-hour screen, normal 100-g 3-hour oral glucose tolerance test), 371 women with mild GDM assigned to usual prenatal care, and 397 women with mild GDM assigned to treatment. Outcomes included: composite adverse perinatal outcome (neonatal death, hypoglycemia, hyperbilirubinemia, hyperinsulinemia, stillbirth, birth trauma), gestational age at delivery, birth weight, and hypertensive disorders of pregnancy. Adjusted regression models included: 100-g 3-hour oral glucose tolerance test results, parity, gestational age, body mass index, maternal age at enrollment, and current tobacco use. Results: The sample of 1,535 women was 68.3% Hispanic and 31.7% non-Hispanic white. Among women with glucose intolerance, Hispanic women had more frequent composite outcome (37% compared with 27%, adjusted odds ratio [OR] 1.62, 95% confidence interval [CI] 1.10-2.37) with more neonatal elevated C-cord peptide (19% compared with 13%, adjusted OR 1.79, 95% CI 1.04-3.08) and neonatal hypoglycemia (21% compared with 13%, adjusted OR 2.04, 95% CI 1.18-3.53). Among women with untreated mild GDM, outcomes were similar by race and ethnicity. Among Hispanic women with treated mild GDM, composite outcome was similar to non-Hispanic white women (35% compared with 25%, adjusted OR 1.62, 95% CI 0.92-2.86), but Hispanic neonates had more frequent hyperinsulinemia (21% compared with 10%, adjusted OR 2.96, 95% CI 1.33-6.60). Conclusion: Individual components of some neonatal outcomes were more frequent in Hispanic neonates, but most perinatal outcomes were similar between Hispanic and non-Hispanic ethnic groups. © 2012 by The American College of Obstetricians and Gynecologists. Published by Lippincott Williams & Wilkins.