In 1986, the National Cancer Institute published its cancer control objectives for the nation, which included projected reductions in breast cancer mortality. The reductions were estimated to be 25.0% from reducing fat, 16.0% from expanding use of breast cancer screening services, and 14.3% from expanding access to state-of-the-art breast cancer treatment. During the same decade, the U.S. population aged and became significantly more ethnically diverse, and accompanying this increase in ethnic diversity was endemic poverty, disproportionately experienced by black and Hispanic minorities. These populations may be seen as medically underserved. With respect to breast cancer, as well as many other cancers, the medically underserved are understudied, not well understood by many in the medical and academic research community, and attended by health care institutions that are under-funded and often do not have the resources necessary to ensure access to state-of-the-art cancer screening, clinical follow-up, diagnosis, and treatment. At the same time, medically underserved women are more likely to be diagnosed with late-stage breast cancer, and some groups (e.g. black women) bear the greatest breast cancer mortality burden in the nation. In this special issue of Breast Cancer Research and Treatment, eight papers describe what we know and what we don't about breast cancer prevention and control in medically underserved populations.