Leaders' behavior can powerfully alter group outcomes. In a programmatic series of preregistered studies, we provide the first rigorous test of whether and why leaders behave differently toward groups of men versus women. In a within-subjects pilot study (N = 336) and in between-subjects Study 1 (N = 368), American adults said they would lead groups of men (vs. women) in a more dominant (e.g., intimidating, controlling) manner. Study 2 (N = 361) replicated this pattern and found that people lead mixed-gender groups similarly to how they lead groups of all women. In Study 3 (N = 314), coaches of boys' (vs. girls') sports teams-real leaders of gender-segregated groups-also said that they led more dominantly. In Study 4 (N = 161), students who believed that they would be leading men (vs. women) were rated by trained coders as more dominant in a videotaped introduction to their group. The pilot study and Studies 1, 2, and 4 all tested for and found evidence suggesting that the underlying mechanism was related to leaders' stereotypes about their followers' communion. In Study 5 (N = 844), men evaluated dominant leaders more positively than women, suggesting that followers may reinforce leaders' tendency to lead men with more dominance. Leaders are likely to treat-and be reinforced for treating-groups of men in a more dominant way, with implications for group outcomes and group members' well-being. (PsycInfo Database Record (c) 2025 APA, all rights reserved).