Plasmacytoid adenocarcinoma of the lung has not been reported. Herein reported is the first case of plasmacytoid adenocarcinoma of the lung. A 68-year-old man presented with cough and sputum. X-P and CT demonstrated a large tumor (10 x 10 x 9 cm) in the right upper lobe. CT-guided needle biopsy was performed. The biopsy showed plasmacytoid malignant cells. The malignant cells were small, had eccentrically located nuclei, perinuclear halo, and basophilic cytoplasm. No mucins were observed by mucins stains. Immunohistochemical study showed that the tumor cells were positive for pancytokeratin AE1/3, pancytokeratin CAM5.2, TTF-1, Ki-67 (labeling 70%), CA19-9, and p53. They were negative for neuron specific enolase, CEA, CD45, CD68, chromogranin, synaptophysin, surfactant apoprotein A, CDX-2, κ-chain, λ-chain, KIT, and PDGFRA. Since epithelial markers and adenocarcinoma markers were positive, the pathological diagnosis was plasmacytoid adenocarcinoma of lung. The patient is now treated with chemotherapy.