OBJECTIVES: This study tested the hypothesis that "structural pluralism" reduces age-standardized mortality rates. Structural pluralism is defined as the potential for political competition in communities. METHODS: US counties were the units of analysis. Multiple regression techniques were used to test the hypothesis. RESULTS: Structural pluralism is a stronger determinant of lower mortality than any of the other variables examined--specifically, income, education, and medical facilities. CONCLUSIONS: These findings support the case for a new structural variable, pluralism, as a possible cause of lower mortality, and they indirectly support the significance of comparable ecologic dimensions, such as social trust.