Although cooperative mating strategies have been observed in other species, the extent to which men and women act to facilitate the mating success of others has been under-researched, especially among unrelated individuals. The present study addressed this gap in knowledge by exploring potential sex differences and individual differences in attitudes toward facilitating and preventing friends’ mating among 256 heterosexual undergraduate men and women. Results showed that women were more likely than men to express attitudes toward preventing the sexuality of friends, whereas no sex difference existed in facilitative mating. For both men and women, positive reciprocity beliefs and high self-perceived mate-value predicted positive attitudes toward facilitative mating. Among women, preventive mating was predicted by low sociosexuality and high intrasexual (within-sex) competitiveness.