A 74-year-old man was admitted with fever, severe cough, and yellow sputum for 1 month. He was diagnosed with lung adenocarcinoma (cT4N2M0, IIIB) 3 months ago and received 2 cycles of pemetrexed-cisplatin adjuvant chemotherapy. He had a history of tuberculosis and a 10-year history of smoking but had quit for 4 years. He maintains a good oral hygiene. Chest Computed tomography (CT) scan showed: (1) multiple lesions in bilateral lobe of the lung; (2) enlarged hilar and mediastinal lymphadenopathy; (3) infection lesions in the lower lobe of the left lung. Repeated sputum acid-fast bacteria (AFB) smear staining was positive. Sputum GeneXpert MTB/RIF assay (Cepheid, Sunnyvale, CA) and culture were positive and sensitive to rifampicin. Considering the retreatment of pulmonary tuberculosis, isoniazid (H), rifampin (R), ethambutol (E), pyrazinamide (Z), moxifloxacin were used as the anti-tuberculosis regimen, and linezolid 600 mg once daily was added to strengthen the regimen. The patient's temperature returned to normal after 5 days of treatment, and cough was significantly resolved after 2 weeks of treatment. However, 12 days after the initiation of linezolid treatment, the patient complained of a black tongue without any other symptoms (Figure 1A). Tongue swab culture showed Enterobacter kobei. Considering that this side effect was related to linezolid, we discontinued linezolid and the tongue discoloration returned to normal within 17 days.