A 70-year-old-woman with idiopathic pulmonary fibrosis (IPF) presented with worsening dyspnea, nonproductive cough and increasing home oxygen requirements over a 24 h period.IPF had been previously diagnosed in accordance with American Thoracic Society guidelines (1); having a consistent clinical presentation, absence of alternative diagnosis and a definite usual interstitial pneumonia pattern on chest computed tomography (CT). History included hemochromatosis, diabetes, hypertension and osteoarthritis. Pirfenidone was initiated two months before presentation. Physical examination revealed clubbing and bilateral basal-predominant fine crackles, consistent with IPF without evidence of heart failure.A routine CT scan of the chest had been performed two days before developing increased dyspnea (Figure 1A) and a repeat contrastenhanced CT chest scan at the time of hospitalization (Figure 1B). There was interval development of diffuse ground-glass opacities (GGO) in both lungs without evidence of pulmonary embolism. Sputum cultures and a nasopharyngeal swab (for polymerase chain reaction) failed to identify bacterial, fungal or viral infection. Bronchoscopy could not be performed due to high oxygen requirements.Treatment with 1 g of intravenous methylprednisilone was given for three days, followed by 50 mg of prednisone. Dyspnea and oxygen requirements returned to baseline. Repeat imaging at one week (Figure 1C) showed interval resolution of GGO. The patient was discharged home with plans to taper off her prednisone over a four-week period.