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新型冠状病毒肺炎（COVID-19）与严重急性呼吸综合征（severe acute respiratory syndrome，SARS）在病原体、临床表现、影像学等多方面存在一定的相似性。两种疾病死亡患者的病理表现也存在相似性。SARS及COVID-19的死亡患者病理均表现为弥漫性肺泡损伤（diffuse alveolar damage, DAD）。SARS患者DAD分期与病程有关，病程≤10~14 d为渗出期，病程>10~14 d为增生期，但渗出及增生、纤维化病变常同时出现，部分表现为急性纤维素性机化性肺炎。肺组织内病毒主要位于肺泡上皮细胞，SARS冠状病毒在体内可存在较长时间。两种疾病均有脾、淋巴结、小血管、心脏、肝、肾等多器官损伤。免疫器官受损可能是低淋巴细胞血症的病理基础，可能影响病毒的清除。部分肺外器官未检测到病毒，提示可能有病毒感染以外的其他机制。病毒损伤与炎症过激导致的免疫损伤相互交织，以及多器官受累、广泛微血栓形成，使病情复杂化，对重症患者的治疗提出了巨大的挑战。

Severe acute respiratory syndrome (SARS) and coronavirus disease 2019 (COVID-19) shared similar pathogenetic, clinical and pathological features. Fever and cough were the most common symptoms of both diseases, while myalgia and diarrhea were less common in patients with COVID-19. Acute respiratory distress syndrome (ARDS) was the most severe pulmonary complication that caused high mortality rate. Histologically, diffuse alveolar damage (DAD) was the most characteristic finding in non-survivors with either SARS or COVID-19. Cases of patients died less than 10-14 days of disease duration demonstrated acute-phase DAD, while cases beyond 10-14 days of disease duration exhibited organizing-phase DAD in SARS. Meanwhile, organization and fibrosis were usually accompanied by exudation. Coronavirus was mostly detected in pneumocytes, but less in macrophages and bronchiolar epithelial cells. Hemorrhagic necrosis and lymphocyte depletion were found in lymph nodes and spleen in both SARS and COVID-19, indicating a pathological basis of lymphocytopenia. Thrombosis was commonly observed in small vessels and microvasculaturr in lungs accompanying DAD. Microthrombosis was also found in extrapulmonary organs in COVID-19, that was less reported in SARS. Damages in multiple extrapulmonary organs were observed, but coronavirus was not detected in some of those organs, indicating an alternative mechanism beyond viral infection, such as hypoxemia, ischemia and cytokine storm induced immunological injury. DAD due to viral infection and immunological injury, as well as multi-organ dysfunction and extensive microthrombus formation, brought huge challenge to the management of patients with severe SARS or COVID-19.