From 1996 through 1998, 18 National Centers of Excellence in Women's Health (CoEs) were designated by the Office on Women's Health (OWH) of the U.S. Department of Health and Human Services (DHHS). These CoEs were charged with developing standards for comprehensive, multidisciplinary, and culturally competent approaches to women's health. One specific mandate to the CoEs was to address the needs of underserved women. This paper presents the efforts of the CoE Racial and Ethnic Minority and Underserved Women Working Group to describe the work done within the CoEs to meet this mandate. One method of defining underserved populations is the seven-point definition used in the current "Index for Primary Care Shortage," which categorizes underserved populations based on characteristics including race, ethnicity, geography, and health outcomes. The definition allows the local identification of underserved communities based on this group of variables. The analysis included in this paper focuses specifically on the CoEs' efforts to operationalize this definition in order to meet the clinical care needs of women who are of low socioeconomic status (SES), racial or ethnic minorities, or non-English speaking. A brief review of the literature linking these characteristics to being underserved is provided, followed by examples of ongoing activities at the 15 currently funded CoEs, to understand the needs of diverse women, to improve the quality of care provided to women, and to address healthcare needs of underserved women who meet this definition. Efforts to serve three additional underserved populations defined by age, sexual orientation, and disability status are also presented.