The trait theory of leadership suggests that personality traits influence leader emergence and effectiveness. While initial empirical evidence supports this perspective the majority of studies have examined the relationship between personality and leadership using self ratings of personality. We believe that this research may underestimate the relationship between personality and leadership. We propose that personality assessed using both self and observer ratings explains more variance in leadership than self ratings of personality alone. Results from 155 participants in leaderless group discussions supported this hypothesis. Further relative weight analysis revealed that observer ratings of extraversion explained the largest percentage of variance in leadership followed by self ratings of openness to experience and observer ratings of openness to experience. Results of two-stage least squares regression analysis showed that the relationship between personality and leadership was mediated by contributions to group success. The implications of these results and directions for future research are discussed.