Practice guidelines, which are assistive tools for clinicians, have a long tradition in clinical medicine. Traditionally, these documents were developed by physicians to improve quality of care and can provide practitioners with valuable medical information and improve objectivity in medical decision making. Guidelines development by nonphysician groups is increasing. Guidelines are now intended to assist in decreasing costs, in reducing liability risk, and in utilization review, among other activities. Despite this enthusiasm for guidelines, their development is variable and validity remains largely untested. The intended clinical and nonclinical applications of guidelines require critical analysis. Practice guidelines are not inherently unethical. However, applications of nonmedical values combined with intense pressures on health care provision create an environment for guideline misuse. The ethical implications of practice guidelines are examined in our article.