Objective To analyze the clinical presentations and radiological characteristics of acute exacerbation of idiopathic pulmonary fibrosis ( IPF) . Methods Clinical and radiological data of 2 patients with acute exacerbation of IPF from April 2006 to July 2008 were retrospectively analyzed and literatures were reviewed. Results Both patients were senior male patients over 60 years old. Dyspnea, cough and inspiratory crackles were the major symptoms and signs. Two patients were experiencing an exacerbation of dyspnea for one week and half of month, respectively. PaO2 /FiO2 of both patients was less than225 mm Hg. In both patients, high-resolution computed tomography ( HRCT) scans at the exacerbation showed typical signs of IPF including peripheral predominant, basal predominant reticular abnormality, with honeycombing and traction bronchiectasis and bronchiolectasis, and newly developing alveolar opacity. HRCT scan showed peripheral area of ground-glass attenuation adjacent to subpleural honeycombing in one patient, and diffusely distributed ground-glass opacity in another patient. Two patients had received corticosteroid treatment. For one patient, the symptoms improved, and ground-glass attenuation adjacent to subpleural honeycombing had almostly resolved. The other patient died of respiratory failure. Conclusions Some acute exacerbation in idiopatic pulmonary fibrosis can be idiopathic. The clinical presentations mainly include the worsening of dyspnea within short time. HRCT generally demonstrates new bilateral ground-glass abnormality with or without areas of consolidation, superimposed on typical changes of IPF.