How can physicians consider patient preferences in reaching medical decisions? Physicians may intuitively agree about the importance of considering all significant aspects of alternative therapies, including patient preferences. However, it may be difficult to resolve or quantitate critical trade-offs between benefit and risk, and quality and quantity of life. One way to do this is decision analysis, a systematic approach to decision making under conditions of uncertainty. Behavioral research involving the assessment of values and probabilities may bear on the adequacy of decision analysis and help us to better understand patient preferences in clinical decisions.