Many patients have uncertain capacity to make decisions about their care. Determining whether a patient possesses decision-making capacity challenges even the most seasoned of physicians. We illustrate an algorithm devised by Miller and Marin (Emerg Med Clin North Am 2000; 18:233-241) that assesses the patient's understanding of his or her condition, ability to process information, and stability of decision-making to determine whether he or she possesses adequate decision-making capacity. Although this algorithm is better than previous approaches, it has limitations and potential problems with its implementation.