Geohelminthiasis is a major health problem in many developing countries. This study was designed to evaluate the role of behaviors and the nutritional status of people with geohelminth infection in two indigenous ethnic groups in lowland Terai, Nepal. One hundred and fourteen individuals (55 Mushar and 59 Tharu) aged 20–60 years participated, and a structured questionnaire was used to investigate socioeconomic status and behaviors. Nutritional status was assessed by anthropometric measurements. Ninety five stool samples of the participants were collected for parasitological analysis. The results showed that the prevalence of geohelminthiasis was 42.1%: 26.3% of the subjects were infected with roundworm, 9.5% with hookworms, and 6.3% with whipworm. Multivariate logistic regression analysis revealed that “not using soap for hand-washing” (adjusted OR = 5.27; 95% CI: 1.41–19.78) and height (adjusted OR = 0.88, 95% CI: 0.79–0.99) were associated with the prevalence of roundworm. “Walking barefoot when outdoor” was associated with the prevalence of hookworm (χ-square test, P = 0.01). Ethnicity was not associated with the prevalence of either of the geohelminths. Because unhygienic behaviors and chronic malnutrition were closely associated with the people's recognition and subsistence pattern, elimination of geohelminth infection in Terai would be possible if deworming campaigns were implemented with in-depth health education and modern agricultural technology. Am. J. Hum. Biol., 2009. © 2008 Wiley-Liss, Inc.