Transsexualism and homosexuality have been theorized to originate in the male from insufficient androgenization of the brain. For verification of this hypothesis clinical science must rely on subjects with an abnormal prenatal/perinatal endocrine history. A case of a 33-year-old 46,XY subject with an incomplete form of androgen insensitivity syndrome (AIS) is presented. In adulthood the only genital sign of masculinization is a clitoris of 4 cm; the vagina is normal size. The diagnosis AIS was verified by androgen receptor studies. At birth there was confusion as to the sex of the newborn. Originally, the subject was assigned to the male sex, but this decision was reversed 5 days after birth and the subject was reared as a girl. At age 30 the subject applied for gender reassignment treatment to the male sex. Upon psychological evaluation the gender identity was unambiguously male and the sexual orientation was exclusively towards women. The estrogen feedback effect on LH, regarded by some as a marker of the sexual differentiation of the neuroendocrinium was negative before orchiectomy but positive after orchiectomy. Our observation demonstrates that in 46,XY subjects a male gender identity and a sexual orientation towards women can develop with a strikingly lower-than-normal level of biological action of androgens.