There is evidence that the lungs of cystic fibrosis (C.F.) babies are normal at birth, and that early lung changes, possibly within the first three months of life, are reversible. Early diagnosis allows the possibility of immunopreventive measures and vigorous treatment of the initial stages of respiratory and gastro-intestinal complications. Since presentation with URTI, for example, has been shown to carry a poor prognosis, early detection through the use of sensitive and specific screening is, therefore, essential. This study reports the results of a seven-year screening programme carried out in the Southern Health Board region of Ireland.