France has decided to add to the national neonatal screening program (Phenylketonuria, Hypothyroidism, Congenital Adrenal Hyperplasia, Sickle cell disease) the screening of cystic fibrosis (CF). The screening of CF will be implemented in all regions of France by the end of 2002 and will cover all newborn (near 800,000/year). Based on the recommendation of the French Screening Foundation, the project has been approved by the Health Ministry and will be financed by the social security. CF neonatal screening is now technically feasible and reliable. The proposed methodology includes: immunoreactive trypsin (IRT) dosage on all newborns at day 3 (by radioimmunology "Cis Bio" or immunofluorescence "Delfia") followed by genotype CFTR analysis if IRT level is above 60 micrograms/L. Screening for 29 mutations is planned. If genotype is negative, control of IRT at day 21 will be obtained. Several requirements are included in the program: a protocol of care for the newly diagnosed CF in a specialised CF center; information to all parents of newborns; results of CFTR genotype has to be given during a clinical visit, even if negative. This screening program should allow to screen 98% of the cystic fibrosis patients before the age of 1 month. In order to ensure perfect efficacy, the CF screening program will be evaluated and modified if necessary.