Self-categorization proponents (e.g., Turner, 1991) assume that group polarization occurs because discussants wish to differentiate themselves from outgroup positions and implicitly think of such groups even when they are not specifically mentioned. Ingroup/outgroup salience is thought to heighten such effects. To examine this view, we had participants discuss Choice Dilemma items either with or without explicit knowledge of outgroup positions. Contrary to a self-categorization account, this manipulation of outgroup salience did not affect the degree of group polarization. In addition, rating measures revealed little spontaneous consideration of outgroup positions on the part of participants, nor was consideration of outgroup positions related to degree of polarization. Group members did show evidence of ingroup identification, but this identification was unrelated to participants' post-discussion conformity to the group consensus. Taken as a whole, these results suggest distinct limits to the self-categorization interpretation of group polarization involving Choice Dilemmas. Copyright © 2006 John Wiley & Sons, Ltd.