The main purpose of the present study was to compare two groups of male homosexuals and heterosexuals in terms of childhood gender nonconformity and fertility rate in a lineage. Two samples of male homosexuals participated in the present study. The first group were Iranian males (258 homosexuals, 179 heterosexuals) aged 18-39 years, living in Iran or abroad and the second group were Iranian males (42 homosexuals, 30 heterosexuals) older than 40, living in Tehran. To gather the data, demographic information, fertility rate in a lineage as well as Childhood Gender Nonconformity-Both (CGN-Both) were used. The results demonstrated that in the two groups of homosexuals, the mean scores of gender nonconformity were significantly higher than heterosexuals. The difference between older-than-forty male homosexuals and heterosexuals was not statistically significant. In the first group, the difference between homosexuals and heterosexuals was significant in fertility rate variables of maternal aunts and women in maternal family. Fertility rate in male homosexuals was higher than male heterosexuals. The difference between two groups of older-than-forty male homosexuals and heterosexuals was significant in the fertility rate of married participants and fertility rate of their sisters. Birth rate in male homosexuals was lower than male heterosexuals and the fertility rate in sisters of male homosexuals was higher than their counterparts. Based on the findings of the present study, it can be concluded that sexual tendency to the same sex in adulthood might be predicted by gender nonconformity in childhood as well as transition of genetic factors.