Research, including animal studies, shows that the fluoride ion (F) adversely impacts the reproductive system in mammals. However, the gene-environment interaction mechanisms involved in this association remain unclear. The objective of the present study was to measure the F level in two regions of Poldasht county, Iran, with low and high drinking water F levels (means 1.90 and 8. 10 mg/L, respectively) and to examine, in females living in the areas, the relationship between the drinking water F and (i) fertility, (ii) infertility without known etiological factors, and (iii) abortion without known etiological factors. Comparing the women in the low and high F areas, the respective rates were: (i) fertility: 105/1993, 5.3%; 70/1224, 0.5%; (ii) infertility without known etiological factors: 17/ 1993, 0.9%; 24/1224, 2.0%; and (iii) abortion without known etiological factors: 6/105, 5.7%; 11/70, 10.0%. We found that there were no statistically significant differences in the reproductive parameters between the low and high F regions when the women were considered by 5-year age groups, but, when the data were pooled and all the age groups were considered together in a group with ages 10–49 yr, those in the low F group were more fertile (p<0.05) and had lower rates of (i ) infertility without known etiological factors (p<0.001) and (ii) abortion without known etiological factors (p<0.001).