Four studies examine how being treated as a sex objects affects women's math and science performance. In Study 1, when female engineering students interact with men who tend to perceive men and women in terms of traditional gender roles these women do worse on an engineering exam. Study 2 demonstrates that when men who tend to perceive women and men in terms of traditional gender roles interact with a female confederate they sit closer to her, have a more open body posture and are viewed by observers as being more sexually motivated. Study 3, demonstrates that when female engineering students interact with a confederate who acts like the traditional men in Study 2, they underperform on an engineering test. Study 4 demonstrates that this underperformance only occurs in gender stereotypic domains and not in non-stereotypic domains. These results suggest that being treated as a sex object can undermine women's performance in stereotypically masculine domains.