The ILO definition of the worst forms of child labour includes work that is likely to jeopardise health and safety. Effective targeting of those child work activities most damaging to health requires both conceptual understanding and empirical evidence of the interactions between child labour and health. The aim of the paper is to review the current state of such knowledge, which is central to the design of policies that, whilst protecting children from work activities most damaging to their health, do not jeopardise the subsistence livelihood of their families. The relationships between child labour and health are complex. They can be direct and indirect, static and dynamic, positive and negative, causal and spurious. The diversity of potential relationships makes their empirical disentanglement a difficult exercise. A conceptual framework of analysis is required and important issues of measurement and of estimation must be given careful consideration.