Primary care physicians frequently have to respond to patients' requirements for medical documentation. Those include certification about fitness and ability to engage in specific activities and about inability to work due to ongoing health problems, which engages physicians' legal and profesionnal responsability. To clarify the rules and modalities of this activity, we present here the legal framework and the good practices. Regarding the sick leave certification, there are well-defined profesionnal and legal guidelines, which is not the case for certification about fitness.