Risks and burdens in the study participation, as well as an adequate risk-benefit balance, are key concepts for the evaluation of clinical studies by research ethics committees (RECs). An adequate assessment and continuous monitoring to ensure compliance of risks and burdens in clinical trials have long been described as a central task in research ethics. However, there is currently no uniform and solid theoretical approach to risk assessment by RECs. Regulatory standards of research ethics such as the Declaration of Helsinki provide only minimal guidance on how risk decisions are considered. Due to discrepancies in the existing literature and guidance documents, adequate risk assessment by RECs remains to be elusive. In this article, we address current definitions of risk and present our own concept of aggregate risk definition. Moreover, we highlight the concept of benefit, the standard of reasonableness with respect to ethics literature and different approaches of risk-benefit assessment. In order to present a comprehensive theoretical approach of risk assessment by RECs, further understanding of the definitions of risk may improve adequate decision-making tasks by RECs. To improve the process of risk assessment by RECs, a dynamic framework will be illustrated, showing step-by-step risk assessment functions. This approach may be a promising tool to ensure adequacy in risk assessment by RECs.