New ethical and professional issues are affecting epidemiology today as a result of the changing social and scientific context in which epidemiology is practiced. These issues arise in interpreting the findings of epidemiologic studies, dealing with potential conflicts of interest, fulfilling obligations to the people studied, publishing study results and providing others access to the data after studies have been completed. The epidemiologist is also faced with new challenges including the need to communicate new information on health risks to non-epidemiologists, and to apply her epidemiologic expertise and study findings to the development of public policy.