We investigated the sex ratio of children of pesticide workers who produced the biocide trichlorophenol and the herbicide 2,4,5-trichlorophenoxy acetic acid from 1961 to 1988 in the city of Ufa, Bashkortostan, Russia. We measured exposure of the two related cohorts to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other dioxins by analyzing 84 blood samples, which produced median TCDD toxic equivalents blood lipid values of 240 ng/kg, which are more than 30 times higher than background or normal exposure from the region. The sex ratio (fraction male) of the combined cohort of 227 children from 150 male and 48 female workers was 0.40, significantly lower (z-test for proportions = 3.21; p < 0.001) than those for the city of Ufa (0.512) and elsewhere worldwide. When we analyzed the sex ratio of the children according to maternal or paternal exposure, we observed a decrease in the number of boys (ratio 0.38) for fathers and a normal number (ratio 0.51) for the mothers. Human exposure of these pesticide producers to high levels of dioxins is associated with the birth of more girls, but only for paternal exposures.