Some patients with Idiopathic Pulmonary Fibrosis (IPF) have disease accelerated deterioration without identifiable cause referred as "acute exacerbation" or "accelerated stage". It is characterized by severe worsening of dyspnea, hypoxemia and new or progressive opacities on imaging studies. The typical histological findings are diffuse alveolar damage in addition to the features of usual interstitial pneumonia pattern. Mortality in this clinical entity is very high and no efficacious therapeutic have been described. The authors describe the clinical, functional and radiological features, treatment and evolution of five patients with IPF acute exacerbation. A discussion will be carry out concerning the IPF acute exacerbation usual features comparing with the alterations noticed in those patients.