Background: Helminth infections continue to pose serious health problems in Thailand. The infections of greatest concern are opisthorchiasis and hookworm. Objectives: We evaluated the prevalence of these infections. The Thai Ministry of Health established a national health plan in 1995 to coordinate health plans for the provincial public health sectors. Methods: A national survey based on probability sampling, interviews, and stool examinations was conducted in 2009 to gather prevalence information of the helminth infections. Results: We found an overall prevalence of helminthiasis among 15,555 Thai people of 18.1%. The highest prevalence was found in the northeastern regions of Thailand. By comparison with previous surveys conducted over the past 5 decades, the prevalence rates have decreased. However, pockets of high infection remain, particularly in the north and northeast of Thailand. Conclusions: Targeted intervention by means of educational programs and public health intervention, and continuing surveillance are indicated.