We explore how team gender composition affects willingness to lead by randomly assigning participants in an experiment to male- or female-majority teams. Irrespective of team gender composition, men are substantially more willing than women to lead their team. The pooled sample, and women separately, are more willing to lead female- than male-majority teams. An analysis of mechanisms reveals that a large share of the negative effect of male-majority teams on women's leadership aspirations is accounted for by a negative effect on women's confidence, influence, and expected support from team members.