A 75-year-old man was referred to our hospital for evaluation of abnormal chest computed tomography (CT) findings. The chest CT had revealed consolidation with ground-glass opacification in the right upper lobe and mediastinal lymphadenopathy. Transbronchial lung biopsy of the consolidation in the right upper lobe did not show malignant cells, and Raoultella ornithinolytica was isolated from the bronchial lavage fluid. We diagnosed the patient with a pulmonary abscess and administered antibiotics. The ground-glass opacification surrounding the consolidation improved; however, mediastinal lymphadenopathy worsened. Endobronchial ultrasound-guided transbronchial needle aspiration of a mediastinal lymph node revealed squamous cell lung carcinoma. Chemotherapy reduced the consolidation in the right upper lobe and the mediastinal lymphadenopathy. It is important to consider lung cancer when pneumonia treatment is ineffective.