A substantial body of prior research documents a gender gap in negotiation performance. Competing accounts suggest that the gap is due either to women’s stereotype-congruent behavior in negotiations or to backlash enacted toward women for stereotype-incongruent behavior. In this article, we use a novel data set of over 2,500 individual negotiators to examine how negotiation performance varies as a function of gender and the strength of one’s alternative to a negotiated agreement. We find that the gender gap in negotiation outcomes exists only when female negotiators have a strong outside option. Furthermore, our large data set allows us to examine an understudied performance outcome, rate of impasse. We find that negotiations in which at least one negotiator is a woman with a strong alternative disproportionately end in impasse, a performance outcome that leaves considerable potential value unallocated. In addition, we find that these gender differences in negotiation performance are not due to gender differences in aspirations, reservation values, or first offers. Overall, these findings are consistent with a backlash account, whereby counterparts are less likely to come to an agreement and therefore reach a potentially worse outcome when one party is a female negotiator empowered by a strong alternative.