The idiopathic interstitial pneumonias (IIPs) represent a subset of interstitial lung diseases of unknown origin. Pulmonary fibrosis is the predominant cause of severe morbidity and mortality in IIPs and increases the risk of lung cancer. Adenocarcinoma and squamous cell carcinoma was identified to be most common in cases of lung cancer with IIP. Here we report a case of pulmonary adenocarcinoma that was almost misdiagnosed as interstitial pneumonia. Our case provides a reference for this unusual presentation and the importance of correct diagnosis and treatment.