The chikungunya outbreak, which significantly affected the populations of Réunion and Mayotte between March 2005 and June 2006, led to the conduct of socio-epidemiological surveys aimed at identifying the objective and subjective factors associated with infection. Analysis of the data collected using a nearly identical questionnaire, administered to representative samples of the local populations (N=1,035 in Réunion, N=888 in Mayotte), revealed a number of similarities between the two islands. The results show that the risk of infection is significantly associated on both islands with socioeconomic status, with the poorest households being substantially more affected than the most affluent households. Environmental variables and sociocognitive variables also appeared to be associated with infection to varying degrees. Among the latter, perceived controllability of risk and perceived utility of prevention seem to have a decisive and cross-cutting influence on protective behaviors. Finally, a multiple correspondence analysis of the various factors related to infection indicates that the “subjective” factors identified in these surveys are not independent of the sociocultural context, which tends to shape perceptions of risk and disease. (R.A.)