Thrombosis with thrombocytopenia syndrome (TTS) induced by the coronavirus disease 2019 vaccine is characterized by thrombocytopenia and thrombosis. Positivity for the anti-platelet factor 4-antibody is related to TTS pathophysiology, similar to heparin-induced thrombocytopenia. Although TTS is very rare, with an incidence of almost 1/100,000 cases, physicians need to keep in mind this adverse reaction that can lead to serious symptoms and death. Prompt treatment should be initiated in cases of suspected TTS.