While highly pertinent to the human welfare consequences of development, the impact of rapid urbanization on population health is not obvious. This paper uses community and individual-level longitudinal data from the China Health and Nutrition Survey to estimate the net health impact of China's unprecedented urbanization. We construct an index of urbanicity from a broad set of community characteristics and define urbanization in terms of movements across the distribution of this index. We use difference-in-differences estimators to identify the treatment effect of urbanization on the self-assessed health of individuals. We find that urbanization raises the probability of reporting of poor health and that a greater degree of urbanization has a larger effect. The effect may, in part, be attributable to changed health expectations, but it also appears to operate through health behaviour. Populations experiencing urbanization tend to consume more fat and smoke more. Copyright © 2011 John Wiley & Sons, Ltd.