This case report describes immune thrombocytopenic purpura in a 41-year-old man hospitalized in the intensive-care unit for COVID-19, 13 days after the onset of COVID-19 symptoms with respiratory failure at admission. Acute respiratory distress syndrome was treated with, among other drugs, low-molecular-weight heparin. On day 8, his platelet count began descending rapidly. On day 10, heparin treatment was replaced by danaparoid sodium, but by day 13, the continued low platelet count made a diagnosis of heparin-induced thrombocytopenia unlikely. Normocytic nonregenerative anemia gradually developed. On day 13, a bone marrow aspiration showed numerous megakaryocytes and a few signs of hemophagocytosis. Corticosteroids were introduced on day 14, and platelets began rising after 3 days and then fell again on day 19. Intravenous immunoglobulin (IV Ig) was then administered. Two days later, the platelet count returned to normal. The immune cause was confirmed by ruling out the differential diagnoses and the excellent and rapid response to intravenous immunoglobulins. Finally, the patient's respiratory state improved. He was discharged to a respiratory rehabilitation unit on day 38. Our case suggests that an immunological cause should be considered in patients with thrombocytopenia during COVID-19.