Sociometer theory (Leary & Baumeister, 2000) proposes that self-esteem is an evolutionary adaptation which functions to monitor the quality and quantity of people’s interpersonal relationships together with their eligibility for these, and to motivate adaptive behaviour in response to these assessments. The present work describes a series of studies designed to systematically test hypotheses concerning relationships between self-perceptions of physical attractiveness, self-esteem and relationship behaviour, derived from sociometer theory. Study 1 extended previous research by employing a novel measure of self-perceived attractiveness and showing that this significantly and positively correlated with both global and multidimensional measures of self-esteem in both women and men. Studies 2 and 3 tested the hypothesis, derived from sociometer theory, that using a social comparison manipulation of self-perceived physical attractiveness should causally affect self-esteem in women. The results of these studies did not support this hypothesis and challenged previous findings in the literature: Women exposed to images of highly attractive others did not report significantly lower subsequent levels of self-esteem than those exposed to unattractive others. Study 4 examined whether exposing women to an implicit manipulation of self-esteem would affect their subsequent self-perceptions of attractiveness. The results showed that women exposed to a negative priming condition reported significantly lower levels of self-esteem and self-perceived physical attractiveness than those in the positive condition. These results constitute the first empirical demonstration that implicit manipulations of self-esteem can exert causal effects on specific self-perceptions. Study 5 examined the previously untested prediction that self-perceptions of desirability and self-esteem would correlate with self reports of romantic relational behaviour in women. The results indicated that although self-perceptions of desirability significantly correlated with relational behaviour, self-esteem did not. These results, together with previous research in self-esteem are discussed in relation to sociometer theory, and a novel modification of the theory is proposed.