The present research tested the prediction that mixed-sex interactions may temporarily impair cognitive functioning. Two studies, in which participants interacted either with a same-sex or opposite-sex other, demonstrated that men's (but not women's) cognitive performance declined following a mixed-sex encounter. In line with our theoretical reasoning, this effect occurred more strongly to the extent that the opposite-sex other was perceived as more attractive (Study 1), and to the extent that participants reported higher levels of impression management motivation (Study 2). Implications for the general role of interpersonal processes in cognitive functioning, and some practical implications, are discussed.