Men's and women's mate preferences impose on each a unique set of adaptive problems that must be solved when judging the desirability of prospective mates. One potentially revealing source of information about an individual's desirability as a romantic partner is contained in the decisions made by same-sex others. The present studies predicted that men's and women's desirability assessments would be affected in opposite ways when target persons were depicted with members of the target's opposite sex. Study 1 (N = 847) documented that women rated men more desirable when shown surrounded by women than when shown alone or with other men (a desirability enhancement effect). In sharp contrast, men rated women less desirable when shown surrounded by men than when shown alone or with women (a desirability diminution effect) . Study 2 (N = 627) demonstrated similar sexually divergent effects for estimates of the desirability of same-sex competitors.