This paper exploits longitudinal data and methods to study the determinants of child immunization in 1990 s China. Many countries such as China are experiencing rapid economic transitions characterized by declining public health expenditures, privatizing health-care sectors, increased inequality and high income growth. It is still poorly understood how such changes affect utilization of preventive health care. Data from three waves of the China Health and Nutrition Survey were used to examine the immunization effects of child, household, and community health facility characteristics, as well as changes of such effects over time. Results indicate that gender and wealth differentials in immunization increased during China's transition, though these effects were small. The most important determinants were service price and maternal education. Wealth effects were minimal, indicating that the long-run effect of economic transition on immunization rates may depend crucially on the extent to which more rapid economic growth leads to increased educational investments. Methodologically, the paper finds substantial bias from standard cross-sectional models in contrast to panel data approaches, adding to the case for expanded collection of longitudinal health data in developing countries.