To estimate the incidence of infl uenza-associated illness, we reviewed passive disease surveillance data collected by the hospital in Maela and collated by the Com- mittee for Coordination of Services for Displaced Persons in Thailand. This surveillance system captured data only on patients visiting the hospital for treatment. The number and incidence rate (calculated by using monthly camp population census data) of clinically diagnosed upper respiratory tract infections (URTIs) and lower respiratory tract infections (LRTIs) were reported by month. No information was available to determine the number of ILI cases; therefore, we could not estimate the proportion of URTIs caused by infl uenza viruses in Maela. However, because most LRTIs reported are likely to be clinical pneumonia, we estimated the incidence of infl uenza-associated pneumonia as the incidence of LRTI multiplied by the percentage of pneumonia patients with specimens positive for infl uenza A. To determine the effect of pandemic (H1N1) 2009 on overall case numbers, we compared 2008 data with 2009 data.