Collaborative decision making occurs whenever two or more individuals contribute their diverse knowledge and expertise to the decision-making process. In medicine, this happens during morning rounds, case conferences, consultations, and elsewhere. This paper presents an analysis of collaborative medical decision making, focusing on two factors that can powerfully influence the kind of information that gets discussed, and hence the nature of the decisions that are made. These are 1) the pre-discussion distribution of problem-relevant information/knowledge, and 2) each participant's awareness of other individuals' knowledge and talents. The authors review previous psychological research on group decision making that concerns these factors, and call attention to several lines of inquiry that might fruitfully be pursued in clinical settings.