The current research investigated biases in attributions of the origins of others' preferences in a group decision situation. In two experiments, students indicated their preferred alternative in a decision on an important issue in their school, and then explained the bases for preferences of those agreeing and disagreeing with them. Results showed that participants saw preferences of those who agreed as more rationally and less externally based than of those who disagreed. This effect increased with perceived issue importance, when the decision was made by in-group representatives, when the decision outcome was concordant with their own preference (Study 1), and, on the externality dimension, when their representatives were in the majority when deciding on an important issue (Study 2). Findings have important implications for our understanding of the tolerance of others and acceptance of group decisions, and ultimately, how group members behave and interact. Copyright © 2009 John Wiley & Sons, Ltd.