Population-based analysis of cesarean section rates within 172 geographic areas in the Commonwealth of Massachusetts during fiscal year 1985 revealed a nearly normal distribution of observed-to-expected rates, implying that the forces that compel obstetricians to perform this surgical procedure are pervasive. However, a small number of areas were identified in which the number of procedures performed was significantly different from the state mean. During fiscal years 1982 to 1985, certain geographic subgroups consistently demonstrated incidence rates significantly greater than the state mean. Although variation (either overutilization or underutilization) from the state rate is not synonymous with inappropriate care, those physicians within the identified geographic areas must take responsibility for ascertaining the explanation for the variance.