There is a growing literature looking at how men and women respond differently to competition. We contribute to this literature by studying gender differences in performance in a high-stakes and male dominated competitive environment, expert chess tournaments. Our findings show that women underperform compared to men of the same ability and that the gender composition of games drives this effect. Using within player variation in the conditionally random gender of their opponent, we find that women earn significantly worse outcomes against male opponents. We examine the mechanisms through which this effect operates by using a unique measure of within game quality of play. We find that the gender composition effect is driven by women playing worse against men, rather than by men playing better against women. The gender of the opponent does not affect a male player’s quality of play. We also find that men persist longer against women before resigning. These results suggest that the gender composition of competitions affects the behavior of both men and women in ways that are detrimental to the performance of women. Lastly, we study the effect of competitive pressure and find that players’ quality of play deteriorates when stakes increase, though we find no differential effect over the gender composition of games.