In a population-based case-control study in Southern Henan Province, central China, children suffering from Japanese encephalitis (JE) were compared with neighborhood controls matched by age and sex in terms of several social and environmental variables. Factors found by crude analysis to be associated with an increased risk of JE included lower family income, lower parental education, living in houses near the periphery of villages and poor quality of houses. When adjustment was made for confounding variables, only the association of house location within village remained of borderline significance (OR = 0.51, 95% CI = 0.15 approximately 1.03). It is suggested that the beneficial effect of higher family income and parental education was partly due to the fact that those parents might be more conscious about having their children vaccinated in the situation where there was a shortage of JE vaccine in the study area.