The preferences of adults with cancer about alternative roles they might play in treatment decision making was examined. The hypothesis was that people with cancer have ideal points along the psychological dimension of keeping, sharing, or giving away control over decision making. A theoretical sample of 60 ambulatory oncology patients was tested using two card-sort procedures with a total of eight vignettes describing various patterns of control over treatment decision making. Results indicated that preference orders of 59/60 patients were consistent with the existence of an underlying psychological dimension, “preferences for control over treatment decision making”; that most patients preferred the pattern of shared control; and that patients preferred to give control to the physician rather than a family member.