A knowledge, attitude, and practice (KAP) survey and an extensive entomologic survey were conducted in two sub-districts of Kamphaeng Phet province, Thailand, to test the hypothesis that correct dengue knowledge and practice reduce dengue vector populations. We found a negative association between respondents' knowledge of preventive measures and the number of unprotected containers in and around their houses. Knowledge of development sites was positively associated with unprotected containers. No relationships existed between knowledge of dengue and adult mosquito reduction practices. A higher number of unprotected containers increased the likelihood of the house being infested with one or more adult Aedes aegypti. Surprisingly, houses of respondents that used mosquito coils or had screening on doors and windows were significantly more likely to be infested (odds ratio =2.0) with adult Ae. aegypti. We conclude that there is a direct link between knowledge on dengue prevention and container protection practices, whereas measures against adult mosquitoes are used only when people experience a mosquito nuisance problem.