Iain Chalmers and the National Perinatal Epidemiology Unit, Oxford, England, developed a comprehensive listing of perinatal care procedures shown to reduce the frequency of adverse outcomes during pregnancy and childbirth. This list was used as a framework for a pilot study conducted in 1992 that reviewed similarities and differences in opinion and practice style between certified nurse-midwives (CNMs) and obstetrician/gynecologists. Twenty CNMs and 57 obstetrician/gynecologists who were active clinical practitioners in San Diego commented on 24 items drawn from Chalmers' work. The CNMs were more likely to favor the availability of social and psychological support variables and to use them in their practice. The groups were more alike than different in their views concerning preventive interventions during the prenatal period. CNMs were more likely to support the availability of alternatives to maternal positions for labor and birth, exhalatory breathing, and delayed pushing and less likely to support the availability of electronic fetal monitoring, epidural anesthesia, episiotomy, and active management of the third stage. A small sample size and limited response rate restricted interpretation and generalizability of these data. Nevertheless the data offer support for other studies with similar findings. They also suggest that health system administrators should inform women and families about differences in practice styles before families select from among the various insurance options that may, in the end, restrict the choice of provider or birth setting.