Understanding the economic burden of illness for households can inform pro-poor health and social protection policy, yet research is in its infancy and appropriate methods require further debate. Quantitative studies are powerful when applied to the right health policy questions, including the measurement of illness cost burden indicators. However, this paper argues that not all dimensions of economic burden can be measured easily, some dimensions relevant to policy, such as social actors' responses to illness and their strategies to cope with illness costs, cannot be reduced to quantitative indicators at all, and large-scale surveys may overlook context-specific processes operating at household level that influence people's paths in and out of poverty as a result of illness. This leaves scope for longitudinal case-study household research to enhance understanding of economic burden and provide additional policy insights on how to better protect households from cost burdens and improve resilience. Drawing on the experience of research in urban Sri Lanka, the paper sets out several comparative advantages of case study research in this area. First, it complemented household survey data by revealing the complex and dynamic nature of illness costs and how these cost patterns (for example, sudden cost peaks) influenced household ability to manage costs. Secondly, it improved understanding of vulnerability or resilience to illness costs by capturing the diverse resources, within and outside the household, used by people to cope with illness costs, and the social institutions and decision-making processes that influenced access to them. Thirdly, the cases enabled the research to develop a picture of the inter-connected factors mediating the impact of illness on livelihood outcomes.