The income inequality hypothesis on the relationship between income inequality and population health has been debated for decades Disagreement exists on the hypothesis because empirical findings have reached inconsistent conclusions. At the cross-national level, the limited number of industrialized nations has created a chronic small-N problem for statistical analyses of the hypothesis. The OECD regional database containing statistics of hundreds of regional units can provide a breakthrough and is used for the first time for multiple regression in this article. It is found that income inequality is a statistically significant determinant of all the health indicators analysed. The findings support the income inequality hypothesis. In addition, the impact of income inequality seems to be stronger on infant mortality than on old-age mortality. GDP per capita also statistically significantly influences both life expectancy and old-age mortality but not infant mortality.
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