Improvements in outcomes for patients who have cystic fibrosis (CF) have been striking in the last 30 years. Median survival now approaches the fifth decade of life. Advances in the understanding of the basic defect and the pathobiology of CF have led to new treatments, some of which have undoubtedly contributed to this success. Improved understanding of the basic defect and the acquisition and maintenance of epidemiologic resources for the CF population in the United States have allowed us to determine predictors of survival and identify genetic, environmental, and therapeutic factors that may influence it. This article reviews some of the key epidemiologic and pathobiologic factors discovered thus far.