163 Background: Previous studies have assessed physician perceptions of practice guidelines and identified barriers to adherence, including lack of knowledge, attitudes, and other factors. Little is known about attitudes toward and use of cancer management guidelines specifically. Methods: We surveyed a random sample of 750 medical oncologists and 750 surgeons drawn from the AMA Masterfile between January and June 2012. 896 responded; 130 of these reported that they had not seen breast cancer patients in the previous year and were asked not to complete the remainder of the survey. We analyzed responses from the remaining 766 (403 surgeons and 363 medical oncologists). Results: Mean participant age was 52; 36% worked in a practice with an academic affiliation. Attitudes towards clinical practice guidelines were generally favorable. Few (<3%) disagreed that guidelines were good educational tools or convenient, and only 12% felt that they were biased, although 24% felt they were oversimplified, 20% found them too rigid, and 20% perceived them as a challenge to physician autonomy. Most agreed that guidelines were intended to improve the quality of care (98%) but opinion split about whether they were intended to decrease costs (51% felt they were). NCCN guidelines were reported to influence the cancer management decisions of 96% of medical oncologists and 70% of surgeons (p<0.001), and ASCO guidelines influenced 65% of medical oncologists and 45% of surgeons (p<0.001). Many respondents looked at the NCCN guidelines at least every few months (93% of medical oncologists, 48% of surgeons, p<0.001). Most respondents reported they made guideline-concordant decisions in the majority of their cancer cases. Yet most respondents reported that they rarely refer patients to the patient versions of the NCCN guidelines (76% refer ¼ or fewer of their patients). When making a guideline-inconsistent recommendation, 17% do not routinely discuss the inconsistency with patients. Conclusions: Attitudes toward physician-directed cancer management guidelines are generally positive, and they are frequently used. However, physicians infrequently advise use of patient versions.