Interstitial lung diseases are a very heterogeneous group of diseases that usually follow a progressive and relentless course that may be interspersed with episodes of rapid progression that are not related to infection, heart failure, or pulmonary thromboembolism. A set of criteria for acute exacerbation of idiopathic pulmonary fibrosis (AEIPF) has been recently proposed. The incidence of AEIPF is not known, but episodes are usually associated with significant morbidity and mortality. The mechanisms that lead to AEIPF are not known, but a prominent role for ongoing alveolar epithelial injury and disordered repair has been suggested. Patients presenting with AEIPF have new opacities on chest radiography, and the pattern of lung involvement may be associated with prognosis. Lung biopsies of AEIPF patients show either a pattern of diffuse alveolar damage or organizing pneumonia. Clinicians should systematically evaluate for infections and other potentially treatable causes such as heart failure and pulmonary embolism. No randomized controlled trials have been conducted on therapies for AEIPF; most patients are treated with initiation or augmentation of immunosuppressant therapy. The role of agents such as pirfenidone and anticoagulants for the prevention or treatment of AEIPF has not been definitely established. Low tidal volume ventilation is a rational strategy during the management of patients with AEIPF requiring mechanical ventilation, and the role of lung transplantation has not been adequately studied in this population. Furthering our understanding on the mechanisms, risk factors, and natural history of AEIPF will be a fundamental step toward the development of effective therapies. © 2011 by Lippincott Williams & Wilkins.