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Retrospective data were entered anonymously by 1,178 adult men using computer-assisted self-interview. Twenty-seven were victims of sister-brother incest (SBI), 119 were victims of child sexual abuse by an adult female (CSA-AF) before 18 years of age, 1,032 were controls. SBI was often the first sexual experience for the victim. Our findings were consistent with other reports of early and persistent hyper-eroticization of incest victims. SBI increased the likelihood of engaging in behaviors as an adult consistent with a co-existing or primary male-male sexual orientation, and SBI and CSA-AF had deleterious impacts on adult men's sexual adjustment with their adult partners. Meiselman (1979, pp. 294-298) found eight cases of brother-sister incest described by sisters (BSI) and three cases sister-brother incest described by brothers (SBI) in her clinical sample. The three SBI victims Meiselman (1979) described had all been harmed by the SBI, but the victims described in two of the three cases also had been victims of incest perpetrated by other family members (the mother in one case and a brother in the other case). Over

Anonymous retrospective data were provided by 3,443 adult participants via computer-assisted self-interview. This was the first study focused on determinants of adult sexual orientation to adjust for the effects of same-sex sibling incest. Five measures of adult sexual orientations (ASOs) provided evidence consistent with the theory that ASOs result from early sex-specific romantic attachment, conditioning caused by early sexual experiences with partners, and other experiences, such as early masturbation using human images, acting synergistically with critical period learning, and sexual imprinting. Early same-sex crushes were the most powerful predictor of ASOs, and they also increased the likelihood of engaging in early samesex partnered and masturbation behaviors. Incestuous experiences with same-sex siblings affected the ASOs of the incest participants. And, lesbian, gay, and bisexual participants tended to have an earlier onset of puberty than heterosexual controls within sexes. However, statistical analyses showed that the incest and puberty effects were mathematically explained by the participant's early sexual experiences with partners and other experiences such as masturbation using human images. Early same-sex crushes were predicted by nuclear family variables implying that samesex crushes were more likely when the opposite-sex parent modeled an unsatisfactory heterosexual romantic partner.

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