Performance measurement has become one of the foundations of current efforts to improve health care quality and has successfully increased compliance with practice guidelines in many settings. Despite the successes of performance measurement, many physicians remain apprehensive about its use because performance measurement "gets in the way of" delivering good care. There are several reasons clinicians might feel this way. First, performance measurement is increasingly being extended to areas that have only a small clinical benefit and thus risk diverting attention from other more important but unmeasured aspects of care. Second, most performance measurement systems provide no priority for following guidelines likely to yield a large clinical benefit compared with guidelines likely to yield at best a small clinical benefit. Third, performance measures focus physicians' attention narrowly on compliance with those measures rather than more broadly on the needs of the individual patient. Because performance measures are evaluated at the level of the indicator, they may crowd out quality at the level of the patient that is equally important but that cannot be easily measured. Performance measures play an important role in improving health care quality and will undoubtedly continue to do so; however, they are only one part of the solution to improving health care quality. Good performance is not necessarily good care, and pressure to improve performance can come at the sacrifice of good care. In its current state, performance measurement is better suited to improving measured care than improving the care of individual patients.