Abstract: In oncology, quality of care is a major issue for patients and providers. Significant variations in care, including nonreceipt of adjuvant systemic therapy, nonadherence to therapy, and/or early discontinuation of therapy, occur frequently and may impact survival. Reasons for these variations are not well understood, but may play a role in the prominent disparity in breast cancer survival between blacks and whites. Since May 2006, the Breast Cancer Quality of Care Study (BQUAL) has recruited 1158 women with nonmetastatic breast cancer from several centers across the country, with completed data on 1057 participants to date. Detailed information on demographic, behavioral, biomedical, and emotional factors related to chemotherapy use was collected on each participant at baseline and at two follow-up interviews during the first 6 months. In addition, for women with ER+ tumors, further questionnaires were completed every 6 months regarding hormonal therapy use. Each participant was also asked to provide a DNA sample, and to allow medical record review. We surveyed physicians providing care to the study participants regarding attitudes toward adjuvant treatment. The mean age of participants was 58 years (SD 11.6), and 15% (n = 160) were black. The majority had an annual household income <$90,000 (n = 683), had college education or higher (n = 802), 55.9% were married, and 57.9% were not currently employed. Seventy-six percent had hormone-receptor-positive tumors, 49.9% initiated chemotherapy and 82.7% started hormonal therapy. Blacks were more likely to have lower annual household income (p < 0001), less education (p = 0.0005), ER negative tumor status (p = 0.02), and poorly differentiated cancer (p = 0.0002). The main endpoints of the study are noninitiation of chemotherapy or hormonal therapy, nonadherence to therapy and early discontinuation of therapy. Treatment and outcomes will be compared on the 15% of participants who are black versus other participants. The BQUAL Study will be a rich ongoing source of information regarding reasons for differences in receipt of both adjuvant chemotherapy and hormonal therapy. This information may be useful in planning interventions to improve quality of care.