Background: Post-COVID-19 systemic inflammatory syndrome is considered to be an aquired immunological disorder, which may develop in some individuals after the remission of infection with SARS-CoV-2 and defined by inflammatory clinical manifestations (fever, arthralgias, cutaneous and mucosal pallor, physical weakness) and modified biological parametres (normochromic normocytic anaemia, increased serum levels of C reactive protein and rheumatoid factor), with no proof of an infectious process, to which corticotherapy may be a suitable therapeutic strategy. Case Report: A 43 year old male was admited in the Department of Internal Medicine for high fever (39,4°C), moderate polyarthralgias and physical weakness, with a negative test result of SARS-CoV-2 RT-PCR. The patient had been previously diagnosed with a moderate-to-severe form of COVID-19, a month prior to the current admission. The patient also experienced transitory dry cough for a month, with no other relevant clinical abnormalities. Upon physical examination, cutaneous and scleral pallor was observed and lung auscultation revealed hardened vesicular murmur bilaterally. Blood analysis revealed normochromic normocytic anaemia and increased serum levels of rheumatoid factor and of C reactive protein, which suggested a nonspecific inflammatory syndrome. Although blood cultures and other microbiological tests were negative for an infectious process, a chest X-ray was performed, which detected the presence of a nodular formation in the superior left lung lobe. Several differential diagnoses were taken into consideration, including pulmonary sarcoidosis and granulomatosis with polyangiitis, both of which were excluded, clinically and biologically. A thoracic computed tomography (CT) was later performed, which revealed the presence of a tumoral nodule in the left lung, associated with multiple mediastinal and supraclavicular lymphadenopathies, indicative of lung cancer. However, lung cancer was also excluded upon the histopathological examination of paratracheal lymphnodes, which detected multiple areas of parenchymal necrosis surrounded by dense inflammatory infiltrates, formed predominantly by histiocytes. All of these findings resulted in the diagnosis of a post-COVID-19 rheumatoid syndrome, the only therapeutic strategy being the administration of high doses of intravenous and oral methylprednisolone, which improved the patient’s health. Conclusion: Post-COVID-19 immunological disturbances should be taken into consideration in patients who experience repetitive clinical and biological inflammatory manifestations after the remission of the infection with SARS-CoV-2, which may be improved through high dose corticosteroid therapy