In an era of increasing competition in medical care, critical pathway guidelines have emerged as one of the most popular new initiatives intended to reduce costs while maintaining or even improving the quality of care. Developed primarily for high-volume hospital diagnoses, critical pathways display goals for patients and provide the corresponding ideal sequence and timing of staff actions for achieving those goals with optimal efficiency. Despite the rapid dissemination of critical pathway programs in hospitals throughout the United States, many uncertainties remain about their development, implementation, and evaluation. In addition, serious concerns have been raised about their effect on patient outcomes and satisfaction with care, physician autonomy, malpractice risks, and the teaching and research missions of many hospitals. Underlying these concerns is the absence of data from controlled trials to evaluate the effects of critical pathways. Physicians should understand the potential benefits and problems associated with critical pathways because physicians are increasingly being asked to provide leadership for pathway programs. Physicians and other health service investigators should also develop methods to study pathways in evolving health care settings. Although the promise of reduced costs and improved quality is enticing, the gaps in our knowledge about critical pathways are extensive; therefore, like any new health care technology, pathway programs should be fully evaluated in order to understand the conditions under which that promise may be fulfilled.