BACKGROUND: Pulmonary fibrosis (PF) is caused by a heterogeneous group of diseases, with a high inter-individual variability in disease trajectory. Identifying disease progression in patients with PF has impact on clinical management decisions. However, strategies to early identify and predict disease progression for these patients are currently lacking. In this study, we aim to assess long-term FVC change in patients with PF measured with home spirometry, and evaluate the feasibility of a multinational patient-led registry in PF. In addition, we will assess validity of patient-reported outcomes (PROMs) for the different subgroups of patients with PF. METHODS: In this international, prospective, multicenter, observational study, we aim to include 700 patients across seven European countries. Patients will monitor their disease course for a period of two years using an online home monitoring program (I-FILE), which includes home spirometry, pulse oximetry, and PROMs. Results will be directly sent to the hospital via the online application. Patients will be asked to perform daily home spirometry and pulse oximetry in the first three months, followed by once weekly measurements for a period of two years. PROMs will be completed in the online I-FILE application every six months, including the King's brief Interstitial Lung Disease Health Status, The EuroQol five dimensions five-level, Visual Analogue Scales on cough, dyspnea, fatigue and general complaints, Leicester Cough Questionnaire, Fatigue Assessment Scale, Work Productivity and Activity Impairment Questionnaire, Global Rating of Change Scale, and Living with Pulmonary Fibrosis questionnaire. DISCUSSION: This study will provide much needed insights in disease trajectories of the different subgroups of patients with PF. Simultaneously, the I-FILE study will yield valuable information on the use and feasibility of home-based data collection. This international patient-led registry will facilitate trans-border collaboration to further optimize care and research for patients with PF. TRIAL REGISTRATION: The study was registered on the 12th of March 2020 in the International Clinical Trial Registry, www. CLINICALTRIALS: gov ; Identifier: NCT04304898.