Idiopathic pulmonary fibrosis (IPF) is an uncommon disease in which the lungs become scarred and stiff for no apparent reason. Patients note shortness of breath and cough, and many eventually die of lung failure. Treatment may include medications to decrease inflammation or further scarring or lung transplantation. How IPF naturally worsens over time is uncertain because the disease is uncommon and many patients receive a diagnosis in more advanced stages of disease. The researchers of this study previously performed a study in which patients with mild to moderate IPF were randomly assigned to take an experimental treatment or a placebo. The study focused on whether patients improved with treatment. However, the researchers realized that observing the patients who took placebo could provide valuable information about what happens over time to patients with untreated IPF.