Since the discovery of the gene associated with cystic fibrosis (CF), there have been considerable advances in our understanding of the mechanisms of disease. Although we are identifying patients with milder manifestations of disease, there are a number of patients who are not diagnosed until adulthood. There is a movement for earlier intervention, so there is increasing interest in making the diagnosis of CF in the asymptomatic patient. With more sophisticated testing, we are able to make the diagnosis in the newborn or even the fetus. In this report, we discuss our current approach to making a diagnosis of CF.