Sexual selection theory provides a powerful model for the analysis of psychological sex differences. This research examined (a) tests of several sex differences in mating psychology predicted from sexual selection theory, (b) broad developmental hypotheses about sex differences in mating psychology--through the relationship of mating psychology to sexual orientation, and (c) the structure of within-sex differences in mating psychology. Scales measuring aspects of mating psychology were administered to heterosexual and homosexual Ss of both sexes. The structure of scale intercorrelations was similar across groups. All scales yielded sex differences consistent with sexual selection theory. Homosexual Ss generally obtained scores similar to those of same-sex heterosexual Ss, though several scales were significantly related to sexual orientation. Findings constrain hypotheses concerning the origins of sex differences.