This study investigates empirically whether the population health benefits arising from progress toward universal health coverage (UHC) vary according to how equitable countries are in alternative domains, including access to care and socioeconomic conditions. We define progress toward UHC as an extended role for pooled prepaid funds in health system financing, as opposed to out-of-pocket spending. We examine panel data covering 17 years and 160 countries through instrumental variable methods to get at the causal effects of pooled health financing and various equity proxies on under-5 mortality rates. Our estimations indicate that the benefits of an increased participation of pooled prepayment in health financing, in terms of reduced under-5 mortality, are generally larger in more equitable countries. From a health system efficiency perspective, the data suggest that more equitable access to the health system can contribute decisively to countries' ability to maximize the health gains from publicly funded investments in the sector. Our results also indicate that the health system will be unable to maximize the gains from transition to UHC in isolation from other areas of government policy, highlighting the need for concerted policy efforts.