The leadership role facilitates group process by structuring group interaction. How leadership affects group performance in GSS settings remains one of the least investigated areas of GSS research. In this study, the presence of a group leader is found to make a significant difference in objective decision quality and satisfaction with the decision process. At the same time, perceived decision quality and consensus are not significantly different in groups with a leader and those without one. A content analysis of comments by group leaders shows that group leaders are effective when making comments on clear group objectives and interaction structure in the early stages of group interaction. In the later stages, however, it becomes more important for group leaders to offer comments encouraging interaction and maintaining group cohesion.