Much medical research including clinical or public health comes from observational studies, that represent 9 of 10 research papers published. The rigour and trustworthiness of research is, in large part, based on a priori planning and documentation of a methodical approach to conduct that is usually reported in a protocol. Scientists are used since decades to elaborate study protocols for the approval from independent ethics committee, well before the study begins. Pre-registration of epidemiologic study protocols on publicly available websites and on scientific journals, however, is a debating issue since few years.1 Among those in favour, some issues have been raised to support the importance of a clearly reported protocol: (i) it allows scientists to carefully plan an observational epidemiologic study and thereby …