There is increasing interest in the use of clinical guidelines as a tool to improve the quality and cost-effectiveness of health care. Yet, relatively little data are available regarding the use of guidelines by health care provider organizations. We developed a written descriptive survey investigating the development, implementation, and evaluation of clinical guidelines that was administered to medical directors or their designees from physician medical groups and independent practice associations. Eighty-seven percent of physician organizations were reported to be developing or implementing clinical guidelines. The reasons most often cited for developing clinical guidelines were quality improvement and cost containment. Local expert opinion or judgment was rated as the most important influence in the development of clinical guidelines, followed by medical and scientific literature and externally developed guidelines. Feedback of information was the most popular method of increasing compliance with clinical guidelines, although 19% of physician organizations reported imposing sanctions on physicians who did not use guidelines. Most of the physician organizations surveyed have embraced clinical guidelines. Local development or adaptation of clinical guidelines may be common. There has been disproportionately little attention paid to guideline implementation and to evaluation of guideline effects relative to their development.