BACKGROUND: In response to the importance of early stage breast carcinoma as a public health concern and to the complexity of the clinical literature devoted to treatment of the disease, the National Institutes of Health has held a series of Consensus Development Conferences on the treatment of early stage breast carcinoma. The authors assessed compliance with standards of care for women treated in two states. METHODS: The authors identified patients diagnosed at 18 randomly selected hospitals (N = 1514) in Massachusetts and at 30 hospitals (N = 1061) in Minnesota. They collected data from medical records, patients, and their surgeons to assess compliance with four indicators of quality of care: radiation therapy after breast-conserving surgery, axillary lymph node dissection, chemotherapy for premenopausal women with positive lymph nodes, and hormonal therapy for postmenopausal women with positive lymph nodes and positive estrogen receptor status. RESULTS: Rates of compliance for 3 of the 4 standards of care were > 80% in both states. Only the rate for hormonal therapy for postmenopausal women was low (< 64%). However, the proportion of these women who received either chemotherapy or hormonal therapy was > 90% in both states. CONCLUSIONS: In the states studied, practice appears to be consistent with the results of national consensus conferences and clinical trials regarding the treatment of early stage breast carcinoma. For practices demonstrated to be associated definitively with better outcomes (for example, chemotherapy for premenopausal women with positive lymph nodes) or to be important with respect to prognosis (axillary lymph node dissection) high rates of compliance were observed.