OBJECTIVES: To estimate risk factors for premature neonates not receiving antenatal steroids in a population-based cohort and to determine whether the gains of a quality-improvement collaborative project on antenatal steroid administration were sustained long-term. METHODS: Clinical data for premature neonates born in 2005-2007 were obtained from the California Perinatal Quality Care Collaborative, which collects data on more than 90% of neonatal admissions in California. Eligible neonates had a birth weight of less than 1,500 g or gestational age less than 34 weeks and were born at a Collaborative hospital. These data were linked to administrative data from California Vital Statistics. Sociodemographic and medical risk factors for not receiving antenatal steroids were determined. We also examined the effect of birth hospital participation in a previous quality-improvement collaborative project. A random effects logistic regression model was used to determine independent risk factors. RESULTS: Of 15,343 eligible neonates, 23.1% did not receive antenatal steroids in 2005-2007. Hispanic mothers (25.6%), mothers younger than age 20 (27.6%), and those without prenatal care (52.2%) were less likely to receive antenatal steroids. Mothers giving birth vaginally (26.8%) and mothers with a diagnosis of fetal distress (26.5%) were also less likely to receive antenatal steroids. Rupture of membranes before delivery and multiple gestations were associated with higher likelihood of antenatal steroid administration. Hospitals that participated in a quality-improvement collaborative in 1999-2000 had higher rates of antenatal steroid administration (85% compared with 69%, P<.001). CONCLUSION: A number of eligible mothers do not receive antenatal steroids. Quality-improvement initiatives to improve antenatal steroid administration could target specific high-risk groups.