The objective of this study was to examine the relationship between indoor environmental factors and acute otitis media in a subtropical area. A case-control study was performed using participants from a prevalence survey that included 219 school children with acute otitis media and 219 age- and gender-matched controls. The study was confined to 4164 primary school children aged 6-12 yr attending 8 primary schools in Kaohsiung rural municipalities who participated in a prevalence study of the health effects of an indoor environment. An acute otitis media case was defined as a child with acute symptoms (presenting with earache, fever, irritability, and/or discharge from the ear) diagnosed by a physician in the previous year. Controls selected from the same school did not have chronic or acute respiratory illness or an ear-related illness during the same period. Information regarding the home environment was obtained using a structured written questionnaire, completed by the parents of the children. Of the many indoor environmental factors included in this study, only living in a home with indications of dampness (mold, flooding, home dampness) showed an association with acute otitis media. It was concluded that dampness in the home is a new public health issue in subtropical areas.