Abstract: Women at risk of being undertreated for breast cancer include women who are older, from minority groups, from lower socioeconomic backgrounds, and those without health insurance or insured by Medicaid. Recent reviews of the cancer care experience of medically underserved populations indicate that breast cancer care may be even less optimal for these populations than the majority of women. These are the same women who may experience difficulty obtaining access to medical care once they are diagnosed with breast cancer. Indirect proof of problems with access is manifested as higher recurrence rates of breast cancer and differences in breast cancer-specific survival among medically underserved women. Multiple factors have been shown to affect access to medical care, and therefore quality of care, including patient-level factors, provider-level factors, and health system factors. This article reviews the current state of these factors in explaining breast cancer care in medically underserved women.