Substituted judgment has been proposed as a method of promoting the autonomy of the mentally incapacitated patient, but little is known about the accuracy of surrogate decision makers in reflecting the true wishes of patients. In this study, surrogate decision makers' views (those of primary care providers and close family members) were compared with the decisions of currently competent chronically ill elderly patients, using a hypothetic cardiopulmonary resuscitation scenario under circumstances of current health and progressive dementia. Concordance between patients and their surrogates was evaluated by assessing percent agreement, kappa coefficient (for concordance beyond chance), and directionality of discrepant responses. Most patient respondents chose to be resuscitated in both scenarios. Although patients predicted that both their physicians (90%) and family members (87%) would accurately represent their wishes, neither family members nor physicians, in fact, were able to adequately predict patients' wishes in both scenarios (kappa less than or equal to 0.3 in all scenarios; percent agreement range, 59% to 88%). Few patients had ever discussed their resuscitation preferences with either their family member (16%) or their physician (7%). These results cast doubt on the usefulness of a strict substituted judgment standard as an approach to medical decision making for patients with diminished mental capacity.