OBJECTIVES: This article addresses the potential impact of the revised standards for race and ethnicity on data from the 2000 census and public health data sources, policies, and programs. METHODS: The authors examine the relationship between race/ethnicity and health in selected measures, identify the factors that influence race/ethnicity identification, consider past experience in race/ethnicity reporting, and explore the challenges in understanding and managing the effects of new racial/ethnic categories in various data sets. RESULTS: The multiple-race group seems to compose only a small percentage of the US population and may have little impact on data for single-race groups. Actual effects will vary according to a number of factors, including the size, composition, and geographic distribution of the group. CONCLUSIONS: More research is needed to support a thorough understanding of the reporting of multirace data and the development of techniques for analyzing these data. Given the importance of understanding the relationship between race/ethnicity and health, the ability to produce useful, comparable, and meaningful data is essential.