The present research examined the effects of information sharing about self-interest and group membership of the negotiation partner on negotiation cognitions, behaviors and outcomes. Study 1 (n = 77) showed that in anticipation of the negotiation, participants placed more trust in an in-group member, and were more willing to exchange information with a negotiation partner who revealed his/her self-interest. Study 2 (n = 80) examined how these effects influenced the development of attitudes and behavior during and after the negotiation. Results showed that negotiations with in-group members were more cooperative when they shared, rather than not shared, information about underlying self-interest. By contrast, negotiations with out-group members were more cooperative when they did not share, rather than shared, information about their underlying self-interest. Copyright © 2006 John Wiley & Sons, Ltd.