Men and women diverge in their political behavior and attitudes. We test whether gender-based variation in political attitudes extends to perceptions of US Supreme Court legitimacy. Using a dataset covering the years 2012–2017, we show that one’s identification as a man or a woman predicts their diffuse support for the Court. In particular, women almost always extend less legitimacy to the Court than men do. This is true within both Republican and Democratic identifiers, and regression analysis shows the gender gap holds when controlling for partisanship, ideology, race, age, education, income, and Supreme Court approval. Additionally, we included a series of questions in a 2021 Cooperative Election Study (CES) module to explore why the gender gap in perceived legitimacy exists. We find that differences in perceptions of the Court’s representation of women and its fairness drive the gender gap in legitimacy.