Historically, dichlorodiphenyltrichloroethane (DDT) was used in northern Thailand for malaria control and farming purposes. Several studies have investigated its effects on end points of adverse reproductive health outcomes. However, the few previous studies investigated hormonal effects in men and available data are inconclusive. The authors aimed to explore the main hypothesis that plasma DDT levels in adult men were associated with reproductive hormone levels. A cross-sectional study was performed of 97 adult men living in a highland village named Mae Sa Mai, 35 km north of Chiang Mai, Thailand. Venous blood samples were collected for measuring plasma levels of DDT and its metabolites and reproductive hormones, including 17beta-estradiol (E2), testosterone, luteinizing hormone (LH), and follicle stimulating hormone (FSH). 1,1-Dichloro-2,2-di(4-chlorophenyl)ethylene (p,p'-DDE) and 1,1,1-trichloro-2,2-di(4-chlorophenyl)ethane (p,p'-DDT) were detected in all plasma samples. p,p'-DDE had the highest level with a median of 4057.7 ng/g lipids and a relatively higher level compared with most other studies. Plasma p,p'-DDT levels were positively associated with years of residence (beta+SE=0.472+0.208, P=0.028) and years of DDT usage for farming (beta+SE=0.177+0.084, P=0.04). The remarkable findings were the negative association of plasma E2 levels with plasma p,p'-DDE levels (beta+SE=-7.093+2.899, P=0.016) and the positive association with plasma 1,1-dichloro-2-(2-chlorophenyl)-2-(4-chlorophynyl)ethylene (o,p'-DDE) levels (beta+SE=16.381+5.596, P=0.008) after adjusting for age and body mass index (BMI). However, these associations were rather weak. Our results suggest that these associations may reflect their different mechanisms of hormonal activities and they would be warrant further detail investigations.