OBJECTIVE: To estimate the relationship between case-mix adjusted cesarean delivery rates and neonatal morbidity and mortality in infants born to low-risk mothers. METHODS: This retrospective cohort study used vital and administrative data for 748,604 California singletons born without congenital abnormalities in 1998-2000. A total of 282 institutions was classified as average-, low-, or high-cesarean delivery hospitals based on their cesarean delivery rate for mothers without a previous cesarean delivery, in labor at term, with no evidence of maternal, fetal, or placental complications. Neonatal mortality, diagnoses, and therapeutic interventions determined by International Classification of Diseases, 9th Revision, Clinical Modification codes, and neonatal length of stay were compared across these hospital groupings. RESULTS: Compared with average-cesarean delivery-rate hospi tals, infants born to low-risk mothers at low-cesarean delivery hospitals had increased fetal hemorrhage, birth asphyxia, meconium aspiration syndrome, feeding problems, and electrolyte abnormalities (P <.02). Infused medication, pressors, transfusion for shock, mechanical ventilation, and length of stay were also increased (P <.001). This suggests that some infants born in low-cesarean delivery hospitals might have benefited from cesarean delivery. Infants delivered at high-cesarean delivery hospitals demonstrated increased fetal hemorrhage, asphyxia, birth trauma, electrolyte abnormalities, and use of mechanical ventilation (P <.001), suggesting that high cesarean delivery rates themselves are not protective. CONCLUSION: Neonatal morbidity is increased in infants born to low-risk women who deliver at both low-and high-cesarean delivery-rate hospitals. The quality of perinatal care should be assessed in these outlier hospitals. METHODS: This retrospective cohort study used vital and administrative data for 748,604 California singletons born without congenital abnormalities in 1998- 2000. A total of 282 institutions was classified as average-, low-, or high-cesarean delivery hospitals based on their cesarean delivery rate for mothers without a previous cesarean delivery, in labor at term, with no evidence of maternal, fetal, or Neonatal mortality, diagnoses, and therapeutic interventions determined by International Classification of Diseases, 9th Revision, Clinical Modification codes, and neonatal length of stay were compared across these hospital groups. RESULTS: Compared with average-cesarean delivery-rate hospi tals, infants born to low-risk mothers at low-cesarean delivery hospitals had increased fetal hemorrhage, birt h asphyxia, meconium aspiration syndrome, feeding problems, and electrolyte abnormalities (P <.02). Infused medication, pressors, transfusion for shock, mechanical ventilation, and length of stay were also increased (P <.001) infants born in low-cesarean delivery hospitals might have benefited from cesarean delivery. Infants delivered at high-cesarean delivery organs demonstrated increased fetal hemorrhage, asphyxia, birth trauma, electrolyte abnormalities, and use of mechanical ventilation (P <.001), suggesting that high cesarean delivery rates said are not protective. CONCLUSION: Neonatal morbidity is increased in infants born to low-risk women who deliver at both low-and high-cesarean delivery-rate hospitals. The quality of perinatal care should be assessed in these outlier hospitals .