The present research reports the results of three studies showing that individuals with a fragile self-concept in the domain of performance are particularly vulnerable to stereotype threat effects. Specifically, women who explicitly described themselves as rather mathematical but whose implicit self-concepts contradicted these claims were vulnerable to stereotype threat effects on mathematical performance. This effect was robust across three studies, independent of the subtleness or content of the stereotype threat manipulation. Additionally, it was shown that the effect was mediated by anxious worrying (Study 3). Copyright © 2012 John Wiley & Sons, Ltd.