Cystic fibrosis (CF) is a life-shortening genetic disease characterized by variability in age of death that is largely due to variability in rate of progression of lung disease, the primary cause of mortality. Recognizing which individuals have more aggressive disease phenotypes and predicting their risk of immediate lung disease progression is a critical step in managing CF lung disease and extending the life expectancy of CF patients. Studies using observational CF patient registries have yielded useful methods for predicting future rate of disease progression and can be used to determine the impact that chronic pulmonary therapies have on slowing rate of lung function decline.