A new Swiss law requires that any research involving humans must aim to answer "a relevant research question". This paper explains the relevance of the relevance criterion in research, analyses the Swiss and British guidelines on relevance, and proposes a framework for researchers and research ethics committee (REC) members that enables a clearer conception of the role of relevance in research. We conclude that research must be either scientifically or societally beneficial in order to qualify as relevant, and RECs therefore cannot avoid reviewing the scientific aspects of proposed studies. Normally only scientifically relevant studies can be of benefit to society, but research of low scientific relevance can nonetheless be relevant to society if it forms part of the education of new doctors and scientists.