This paper provides experimental evidence on the effect of affirmative action (AA). In particular, we investigate whether affirmative action has a ”stereotype threat effect” – that is, whether AA cues a negative stereotype that leads individuals to conform to the stereotype and adversely affects their performance. Stereotype threat has been shown in the literature to be potentially significant for individuals who identify strongly with the domain of the stereotype and who engage in complex stereotype-relevant tasks. We therefore explore this question in the context of gender-based AA for a complex math task. In this context, the stereotype is most relevant for women with high math ability, and the stereotype threat effects can be expected to work in the opposite direction to AA’s competition effect that encourages women to compete. We find that, consistent with the presence of a stereotype threat, AA has an overall negative effect on the performance of high-ability women performing complex math tasks.