The national health insurance proposed for South Africa aims to achieve a universal health system. The best way to identify the financing mechanism that is best suited to achieving this goal is to consider international evidence on funding in universal health systems. The evidence from Organisation for Economic Cooperation and Development countries and a number of middle-income countries that have achieved universal coverage clearly indicates that mandatory pre-payment financing mechanisms (i.e. general tax funding, in some cases supplemented by mandatory health insurance) must dominate, with a clearly specified, complementary role for voluntary or private health insurance.