OBJECTIVE To determine whether the Institute Of Medicine's (IOM) 2009 guidelines for weight-gain during pregnancy are predictive of maternal and infant outcomes in ethnic minority populations. METHODS We designed a population-based study using administrative data on 181,948 women who delivered live singleton births in Washington State between 2006-2008. We examined risks of gestational hypertension, preeclampsia/eclampsia, cesarean delivery, and extended hospital stay in White, Black, Native-American, East-Asian, Hispanic, South-Asian and Hawaiian/Pacific islander women according to whether they gained more or less weight during pregnancy than recommended by IOM guidelines. We also examined risks of neonatal outcomes including Apgar score <7 at 5 min, admission to NICU, requirement for ventilation, and a diagnosis of small or large for gestational age at birth. RESULTS Gaining too much weight was associated with increased odds for gestational hypertension (adjusted OR (aOR) ranged between 1.53-2.22), preeclampsia/eclampsia (aOR 1.44-1.81), cesarean delivery (aOR 1.07-1.38) and extended hospital stay (aOR 1.06-1.28) in all ethnic groups. Gaining too little weight was associated with decreased odds for gestational hypertension and delivery by cesarean section in Whites, Blacks and Hispanics. Gaining less weight or more weight than recommended was associated with increased odds for small for gestational age and large for gestational age infants respectively, in all ethnic groups. CONCLUSIONS Adherence to the 2009 IOM guidelines for weight gain during pregnancy reduces risk for various adverse maternal outcomes in all ethnic groups studied. However, the guidelines were less predictive of infant outcomes with the exception of small and large for gestational age. ABBREVIATIONS GWG: Gestational weight gain; IOM/NRC; Institute of Medicine and National Research Council; NICU: Neonatal intensive care need for ventilation; SGA: Small for gestational age; LGA: Large for gestational age; BERD: Birth Events Records Database; CHARS: Comprehensive Hospital Discharge Abstract Reporting System; ICD: International Classification of Disease; LMP: Last menstrual period; OR: Odds ratio.