Idiopathic pulmonary fibrosis (IPF) is associated with a poor prognosis, although considerable interpatient heterogeneity may be observed. Baseline dyspnea, lung function abnormalities, and gas exchange impairments are predictive of outcome, but recent evidence suggests the change in these parameters over time is as predictive, and in some cases more predictive, of outcome. A change in forced vital capacity> or= 10% may be an important surrogate marker for mortality risk in IPF patients. Histologic analysis shows the deposition of interstitial connective tissue and granulation tissue leading to formation of fibroblastic foci. Thus, ongoing epithelial damage and repair processes associated with persistent fibroblastic proliferation seem important in IPF natural history.