Background: The fatal toxicity of anti-PD-1/PD-L1 agents is pneumonitis. The diagnosis consists of the history of immunotherapy, clinical symptoms and presentation of computed tomography (CT) imaging. The typical CT findings include ground-glass opacities. Based on the similar radiographic feature with 2019 Novel Coronavirus (COVID-19) pneumonia, clinicians are cautious to evaluate diagnosis especially in COVID-19 epidemic areas. Case presentation: Herein we report a 67-year-old male patient

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... h advanced non-small cell lung cancer developed pneumonitis post Sintilimab injection. The dyspnea appeared at the 15th day of close contact with his son who returned from Wuhan, but not accompanied with fever. The chest CT indicated peripherally subpleural lattice opacities at the inferior right lung lobe and bilateral thoracic infusion. The real-time reverse-transcription polymerase-chain-reaction (RT-PCR) from double swab samples within 72 hours remained negative. The patient was thereafter treated with prednisolone and antibiotics for over two weeks. Thereafter the chest CT demonstrated the former lesion almost absorbed, in line with prominently falling CRP level. The anti-PD-1 related pneumonitis with bacterial infection was diagnosed finally based on the clinical evidence and good response to the prednisolone and antibiotics. Conclusion: Both ani-PD-1 related pneumonitis and COVID-19 pneumonia harbor the common clinical symptom and the varied features of CT imaging. Differential diagnosis was based on the epidemiological and immunotherapy histories, RT-PCR tests. The response to glucocorticoid can indirectly help the diagnosis.