BackgroundRoughly 40% of multilateral funding is given through so-called multi-bi aid according to an Organisation for Economic Co-operation and Development's Development Assistance Committee report. Multi-bi aid is the practice of donors voluntarily choosing to direct non-core funding—earmarked for specific sectors, themes, countries, or regions—through multilateral agencies. The funding passes through multilateral channels but in fact is more bilaterally controlled. Examples of multi-bi aid include voluntary contributions within WHO, trust funds within World Bank, the Global Fund to Fight HIV/AIDS, TB, and Malaria, and the GAVI Alliance. Most analyses have shown that development assistance for health has not decreased as a result of the global economic crisis of 2008–10, but these analyses have not established whether important reallocations have occurred between different funding channels. We investigated whether voluntary channels have been more or less consistent than assessed contributions based on the assumption that the withdrawal of assessed contributions is more difficult because of the membership and voting rights that are linked to them. We also test whether multi-bi aid flows have increased or decreased as a proportion of overall global health funding. MethodsWe used data for development assistance for health from 2002–09 collected from the Institute for Health Metrics and Evaluation. We categorised disbursements of development assistance for health by all Organisation for Economic Co-operation and Development countries and the Bill and Melinda Gates Foundation as being either traditional bilateral, traditional multilateral (WHO and World Bank), or multi-bi (Global Fund, GAVI, and UNAIDS). We tested by time series methods whether funding trends for each channel deviated after the onset of the global financial crisis (donations made in 2008, or 2009). FindingsSince 2002, global health donors have increasingly prioritised multi-bi aid at the expense of more traditional forms of multilateral aid (measured as a proportion of all development assistance for health). Multi-bi aid increased as a proportion of all aid by 1·5–2·0 percentage points while bilateral aid as a share of total development assistance for health remained stable over this period, ranging from 62% to 68%. The trend towards multi-bi aid reversed after the onset of the global financial crisis, with donors decreasing their contributions to GAVI, the Global Fund, and UNAIDS by 6 percentage points since 2008. The ten largest global health donors decreased multi-bi aid by nearly 6% as a proportion of all development assistance for health during 2008–09. InterpretationSeveral calls have been made to increase the proportion of funding to newer funding mechanisms such as the Global Fund and GAVI Alliance. Such calls emphasise the importance of short-term global health goals, such as keeping people on treatment, or getting children vaccinated. Our study supports the argument that this type of financing arrangement—although attractive to donors in the short term—creates financial uncertainty and thus hinders the ability of new multilateral health institutions to maintain funding. FundingNone.