INTRODUCTIONPolyserositis is described as infl ammation with eff usion of more than one serous membrane. There is very little published literature linking it to COVID-19 as a late complication.OBJECTIVE Present and describe a case of post-COVID-19 polyserositis.METHODS Data were collected from the medical record of a female patient admitted for fainting spells and marked weakness. The patient underwent a clinical evaluation, additional hematology, imaging and histopathology tests, and a surgical procedure. RESULTSWe present the case of a 57-year-old female patient admitted to hospital for fainting spells and marked weakness, four months after COVID-19 infection. She also had a history of obesity, asthma, type 2 diabetes mellitus and a cholecystectomy in December 1992 for gallstones. Clinical assessment revealed pericardial eff usion and bilateral pleural eff usion, in addition to a tumor-like lesion outside the pericardium, proximal to the right ventricular wall. A surgical procedure and fi ndings from additional tests led to diagnoses of thymic remnants and polyserositis.CONCLUSIONS This is a case of polyserositis in a post-COVID-19 patient. After other causes of polyserositis were ruled out, and since there is a likely physiological and pathogenic mechanism operating between the two diseases, the polyserositis was determined to be a late complication of COVID-19. To date, it is the second case reported in the world and the fi rst reported in Cuba.