The purpose of this study was to explore the hypothesis that women with breast cancer had specific preferences about the degree of control they wanted over treatment decision making. One hundred fifty women, newly diagnosed with breast cancer, were interviewed and their preferences for participation in treatment decision making were established using a measurement tool designed to elicit decision-making preferences (Degner LF, Sloan JF. Decision making during serious illness: What role do patients really want to play? J Clin Epidemiol 1992;45:944-50). Two hundred women with benign breast disease served as a descriptive comparison group. Unfolding theory (Coombs CH. A theory of data. New York: John Wiley & Sons, 1964) provided a means of analyzing the data so that the degree of control preferred by each woman could be established. The majority of the newly diagnosed women preferred to play a passive role in treatment decision making, leaving the decision-making responsibility to their physician, whereas the benign control group preferred a collaborative role in which joint decisions could be made between the patient and the physician. The implications of the results for patient participation are discussed.