This retrospective study was designed to determine the influence of nurses' care during labor and delivery on the cesarean birth rate of healthy, nulliparous women. Labor and delivery nurses in a large, nonprofit hospital were grouped according to the cesarean birth rates of their healthy, nulliparous patients in spontaneous labor. Large differences in cesarean birth rates between nurses in the lowest quintile (near 4.9%) and the highest quintile (near 19%) were not explained by differences in maternal age and gravidity, attendance of mother at childbirth class, insurance status, reliance on public assistance, physician who attended labor, use of epidural anesthesia, augmentation of labor, dilation when the nurse assumed care, infant weight, or gestational age. In multivariate analysis, the elapsed time between when the nurse assumed care and birth was significantly shorter for patients of nurses in the lowest quintile of cesarean birth rate (4.4 hrs) compared with patients of nurses in the highest quintile (5.6 hrs). The former were also less likely to have forceps used to assist vaginal delivery than the latter (13% vs 26%). Nurses in the lowest quintile of cesarean birth rates were more likely to use a form to record psychosocial data than nurses in the highest quintile (35% vs 15%). The study suggests that nurses' care during labor is an important factor influencing cesarean birth rates.