Relational aggression among women presents an overlooked barrier to women's quest for advancement in the workplace. Although research on women's leadership extols their ability to collaborate and form lasting, supportive relationships, one cannot assume that all women are supportive of other women. Research reveals that relational aggression, including professional sabotage, occurs among women in the workplace. Although the number of women who engage in aggression is small, the damage they inflict on other women's reputations, careers, and emotional well-being is great. Collectively, their behavior contributes to erroneous perceptions of women's ability to lead and to engage in productive teamwork. This paper explores the impact of relational aggression on women's advancement in leadership and suggests strategies to mitigate the problem.