Idiopathic Pulmonary Fibrosis (IPF) is a chronic, fibrosing, and progressive lung disease of unknown cause, whose incidence increases proportionally from the age of 60. It is characterized by a poor prognosis. Antifibrotic therapy can slow the progression of the disease and reduce mortality, but the life expectancy is less than 7-10 years in the vast majority of patients with IPF. There are no studies in the literature that have evaluated the presence of small airway disease in patients with IPF prior to the initiation of pharmacological therapy, using the nitrogen washout test. This test is currently considered the only non-invasive method capable of detecting ventilation inhomogeneity and closing volume, which are indicators of small airway dysfunction. The investigators carried out an Italian prospective, observational, multicenter study with the primary aim to assess the prevalence of small airway disease measured by the nitrogen washout test (evaluating the following functional parameters: phase 3 slope, closing volume, closing capacity, closing volume/vital capacity, closing capacity/total lung capacity, and phase 4 slope) in a group of patients with IPF at the time of diagnosis, before the initiation of antifibrotic therapy. During outpatients visits clinical, functional and radiological data will be collected. Results will be compared to an healthy control group matched with IPF population. Variations in small airways disease parameters will be assessed after one year of antifibrotic treatment.