[Ethical issues in longitudinal studies: the case of ELSA-Brasil]

The debate about ethics in research with human beings has historically emphasized experimental studies because of their greater potential to harm the subjects involved. However, observational studies also include risks and relevant questions to be discussed. This article aims to present and discuss the ethical aspects involved in the implementation of ELSA-Brasil, a longitudinal multicenter study, with public funding, in which the research subjects and investigators are employees of the same institutions. The procedures adopted to meet the ethical requirements and commitments are described, as well as the casuistics that guided the actions according to their guiding principles (beneficence, autonomy and social justice). We present some moral problems that required consideration of risks and benefits at the confluence with the study's objectives, and we conclude with comments on the peculiarities and the potential benefits of a longitudinal study.