American black women have a risk of developing breast cancer lower than that of American white women. but they have a worse prognosis when they do develop the disease. A major factor responsible for this discrepancy is a relatively high poverty level in the black population, with the consequent likelihood of delayed diagnosis and presentation with more advanced disease. However, breast cancer in black women also occurs at a younger age, more often is estrogen receptor-negative, and more frequently exhibits aggressive biological behavior as judged by histopathologic grade, high tumor cell proliferation rate, and altered p53 expression. Obesity, known to be associated with a poor prognosis primarily as a consequence of increased estrogen production and bioavailability, is more common in black than in white breast cancer patients. An additional factor may be an earlier age at first completed pregnancy for black women, which is associated with a reduced breast cancer risk but also a poorer prognosis. Both the epidemiologic features and the tumor biology of breast cancer in black women serve to stress the particular importance of developing effective, specifically tailored strategies for early diagnosis in this ethnic group.