Pulmonary fibrosis is an extra-articular manifestation of rheumatoid arthritis whose etiology remains uncertain. Although the clinical course of many individuals with this disorder can mimic that observed in patients with idiopathic pulmonary fibrosis, the natural history of fibrotic lung disease associated with rheumatoid arthritis remains largely undefined. It is the intent of this clinical protocol to (1) estimate the prevalence of pulmonary fibrosis in individuals with rheumatoid arthritis, (2) define the natural history of pulmonary fibrosis in patients with rheumatoid arthritis, (3) estimate the survival rate of individuals with pulmonary fibrosis and rheumatoid arthritis, and (4) examine pulmonary physiologic, radiologic, and biochemical markers that predict the development or progression of fibrotic lung disease.