Neonatal Screening (NBS) is a mass screening, secondary prevention policy aimed at detecting one or several often congenital disorders in all neonates in a given country. The French CF NBS programme is completely functional since the middle of 2003. Drawing its inspiration from the socio-material approach, this article advances a description and analysis of the interactions between the biomedical technologies used in neonatal cystic fibrosis screening and the resulting changes in clinical practice, the bioethical debate and finally in the interstice between voluntary individual consent to screening and the management of a population’s health. The analysis grid focuses on four dimensions: institutional, techno-scientific, regulatory and socio-professional. Backed up by a field survey conducted in the specialised healthcare centres, this study explores two major aspects of the repercussions of NBS: first, the genesis and institutionalisation of this public policy and the impact of a more flexible form of Evidence Based Medicine (EBM) and the sustained controversy on the neonatal screening programme uniting the community of cystic fibrosis paediatrics. This study suggests that institutional stability remains fragile and in this respect constitutes a paradoxical form of production with incompleteness and uncertainty as constituting factors.