A voluntary system of regionalized perinatal health care was developed in Iowa to provide accessible services for a rural population. Larger community hospitals were upgraded to serve as level II regional centers and small obstetric units continued to provide maternity services for low risk patients. Consolidation of services was encouraged only when accessibility was not compromised. Education rather than legislative fiat was the stimulus for change. Evaluation by review of birth and mortality data suggests that a stratified system of care exists in Iowa. Judged by mortality statistics, perinatal outcome has improved since the inception of the program in 1973. The concept of a mortality risk ratio (neonatal deaths/<1,500 gm live births) is suggested as a method of reviewing mortality data from the perspective of risks inherent in the population served.