This paper explores barriers to the use of standard screening and breast cancer treatment that result in systematic differences in health outcomes. We review available data on individual, socioeconomic, and health system determinants of access to standard breast cancer care, including screening, diagnostic, and treatment services. Based on this review, we discuss the combination of factors which result in underservice. We argue that a broad framework which considers health system and social class as well as individual factors is useful for analyzing how structures of health care delivery tend to provide less than standard care to women who are older, have less income, or are less educated, black, or Hispanic. Data collection efforts which do not include structural and socioeconomic variables may result in an incomplete or misleading understanding of the determinants of underservice. These factors also need to be considered in the design and evaluation of public health policies and interventions meant to ameliorate the effects of underservice.