A random sample of 5,182 adults from 6 U.S. metropolitan areas were questioned about incestuous sexual relationships during childhood. Incest was disproportionately reported by both male and female bisexuals and homosexuals. 148 gays (7.7% of the sample) reported 14 (50%) of same-sex, and 7 (22%) of opposite-sex incestuous experiences, and 20 (69%) of same-sex and 2 (3%) of opposite-sex sexual experiences with other relatives. 88 lesbians (3% of the sample) reported 2 (33%) of same-sex incest and 7 (9%) of opposite-sex incest and 1 (17%) of same-sex and 10 (13%) of opposite-sex sexual experiences with other relatives. 12% of 98 male homosexuals vs 0.8% of 1,224 male heterosexuals with a brother reported brother-brother incest. These findings are consonant with those of other studies in which disproportionately more incest by homosexuals was reported. As opposed to an evolutionary genetic hypothesis, these data support the alternative that homosexuality may be learned, since homosexuals do not produce children at sustainable levels and the incidence of homosexuality varies as a function of various social factors. Incest cannot be excluded as a significant basis for homosexuality.