Purpose: To investigate how involvement preferences of patients with breast cancer change during the treatment decision-making process and determine the impact of meeting patients' expectations on decision-making outcomes. Patients and Methods: Participants were 683 patients with breast cancer from 62 oncologists in five different countries recruited to an International Breast Cancer Study Group (IBCSG 33-03) project. Questionnaires elicited patients' pre- and postconsultation preferences for involvement in treatment decision making and whether these were met or not. Decision-related outcomes were assessed postconsultation. Results: Before the consultation, most patients preferred shared or patient-directed treatment decision making. After the consultation, 43% of patients' preferences changed, and most shifted toward patient-directed decisions. The actual postconsultation decision was more likely to be made according to postconsultation rather than preconsultation preferences. Compared with patients who were less involved than they had hoped to be, patients who were as involved as they had hoped to be or were even more involved in decision making had significantly better decision-related outcomes. This was true regardless of whether preference change occurred. Conclusion: Many patients with early-stage breast cancer have treatment options and approach treatment decisions with a desire for decisional control, which may increase after their consultation. Patients' ultimate involvement preferences were more likely to be consistent with the way the decision was actually made, suggesting that patients need to feel concordance between their preference and the actual decision. Patients who directed decisions, even if more than they hoped for, fared better on all decision-related outcomes. These results emphasize the need for oncologists to endorse and facilitate patient participation in treatment decision making.