Three studies investigated the relationship between gender-related traits and sexual orientation. Study 1 showed that gay men and lesbians in an unselected sample of 721 college students differed from same-sex heterosexuals most strongly on gender diagnosticity (GD) measures, which assess male- versus female-typicality of interests (effect sizes of 2.70 for men and .96 for women) and least strongly on measures of instrumentality (I) and expressiveness (E). In Study 2, GD measures showed large differences between 95 gay and 136 heterosexual men (effect sizes of 1.61 and 1.83) and between 46 lesbian and 225 heterosexual women (effect sizes of .98 and 1.28), whereas I and E showed much smaller differences. In Study 3, GD showed large differences between 90 gay and 81 heterosexual men (effect sizes of 1.76 and 1.97) and between 82 lesbians and 108 heterosexual women (effect sizes 1.67 and 1.70), whereas I and E showed much smaller differences. Using data from Studies 2 and 3, ‘gay-heterosexual diagnosticity’ measures were computed for men and ‘lesbian-heterosexual diagnosticity’ measures for women, based on occupational and hobby preferences. These measures correlated very strongly with GD measures.