Guidelines have rather quickly assumed a central role in health care delivery in the U.S. They have become the foundation on which performance measures are built and, therefore, a major player in assessing the quality of care provided by individuals and institutions, the ramifications of which involve reputation,reimbursement, and litigation. We are concerned, however, that in our enthusiasm for collectively endorsing these guidelines, we are marginalizing the importance of physician judgment and inadvertently risking the conversion of guidelines into "cookbooks." We believe that this editorial, while unequivocally acknowledging the fundamental importance of guidelines, simultaneously provides a critically important perspective on the potential for misuse of both guidelines and performance measures. Further, we hope that publication of this commentary will help temper enthusiasm for overzealous conversion of guidelines into performance measures, thereby restoring the vital role of physician judgment and insight into patient management.