Two surveys were conducted to determine what roles people actually want to assume in selecting cancer treatments. 436 newly diagnosed cancer patients and 482 members of the general public participated. Preferences were elicited using two card sort procedures, each of which described five potential roles in decision making. Findings suggested that the impact of being diagnosed with a life-threatening illness may influence preferences to participate. The majority (59%) of patients wanted physicians to make treatment decisions on their behalf, but 64% of the public thought they would want to select their own treatment if they developed cancer. Most patients (51%) and members of the public (46%) wanted their physician and family to share responsibility for decision making if they were too ill to participate. Sociodemographic variables accounted for only 15% of variance in preferences. These variables are not particularly useful in making predictions about which groups want more or less active roles in medical decision making.