We examine the effects of leader prevention focus on the leader’s own behavior, in the form of the harmful overruling of good ideas by their follower team, and on the team’s collective behaviors, processes, and performance. We argue that when leaders adopt a prevention mindset, it can have costly effects on team outcomes. We tested our hypotheses using an experimental design in which 84 five-person teams engaged in a networked simulation, and we manipulated leader prevention focus through selection and training. Our hypotheses were generally supported. Specifically, we found that leaders with a prevention focus are more likely to engage in the faulty overruling of their team’s decisions, causing the team to miss opportunities. We also found that teams with prevention-focused leaders tend to achieve lower levels of performance gains and we test the role of three mediating processes and states that convey the effects of leader prevention focus on reduced performance gains: increased risk avoidance, reduced team prospecting, and lower positive team affective tone. We show support for the mediating role of both reduced team prospecting and lower positive team affective tone. Finally, we show that team member reward responsiveness moderates the effects of leader prevention focus on team risk avoidance and prospecting. We discuss the theoretical and managerial implications of our findings.