Public funders of health research have been widely criticized on the grounds that their allocations of funding for disease-specific research do not reflect the relative burdens imposed by different diseases. For example, the US National Institutes of Health spends a much greater fraction of its budget on HIV/aids research and a much smaller fraction on migraine research than their relative contribution to the US burden of disease would suggest. Implicit in this criticism is a normative claim: Insofar as the scientific (...) opportunities are equal, each patient merits research into their condition proportional to the burden of disease for which that condition is responsible. This claim—the proportional view—is widely accepted but has never been fully specified or defended. In this paper, I explain what is required to specify the view, attempt to do so in the most charitable way, and then critically evaluate its normative underpinnings. I conclude that a severity-weighted proportional view is defensible. I close by drawing out five key lessons of my analysis for health research priority-setting. (shrink)