Since most cancer is treated in the local community, the judgments of primary care physicians about treatment of breast cancer are important. This study examined physician and practice characteristics associated with physician judgments about the treatment of Stage I and Stage II breast cancer. Data are combined from samples of 3,436 physicians: physicians affiliated with hospitals participating in the Community Clinical Oncology Program (CCOP) and a national sample of non-CCOP physicians. This study focused on 1,460 physicians who had seen breast cancer patients and participated in treatment decision-making. Judgments were elicited using brief vignettes. Judgments were more variable for Stage I than for Stage II treatments. Judgments consistent with the NIH Consensus Conferences on breast cancer were more likely from surgeons, physicians who participated in information networks focused on cancer, and those with more breast cancer patients. Concurrence with the consensus conference positions was less likely in older physicians and those in solo practice. These findings point to structures that reinforce quality of care, particularly those that enhance communication, such as group practice or the activities of hospital staffs, information networks, and organized continuing education.