Costa Rica was classified in 1964 by WHO as one of the countries where the eradication of Aedes aegypti was complete, but in 1984 it became reinfested with the mosquito and in 1993 the presence of dengue fever by internal transmission was confirmed, and an epidemic ensued. When widespread flooding in the south of the country resulted from a hurricane in 1996 further outbreaks of dengue were feared. The Health Ministry, with support from UNICEF conducted a campaign to reduce the risk of dengue during and after the disaster. This study, supported by UNICEF, was conducted to measure the impact of that campaign. It was found that the flooding did not increase the incidence of dengue in the region. In fact the epidemic decreased rapidly after the floods both in areas that were inundated and areas that were not. This raised the question of whether the decrease was due, at least in part, to the epidemic having run its normal cycle and been in rapid decline at the time of the disaster. It is logical to conclude, however, that the campaign did have an effect on interrupting the epidemic and preventing its re-emergence. The study produced recommendations for minimizing the chances of a second epidemic with emphasis on vector and environmental control.