A breakdown in leadership is one frequently cited reason for the high failure rate of business process reengineering (BPR) projects. Although past reports suggest that trust plays a key role in whether BPR projects succeed or fail, we lacked a theoretical framework that examines the relationships between trust, leadership effectiveness and BPR outcome. Using theories from the leadership and trust literature, this paper empirically assesses the impact of trust on leadership effectiveness over time. It looks at the evolution of eight BPR projects in a large multinational financial services firm. The study provides evidence that a lack of trust has a downward spiral effect that could result in BPR failure. Conversely, its presence has an upward spiral effect that could result in success. The results show that trust tends to diffuse in BPR projects.