Immune thrombocytopenia (ITP) is an autoimmune condition associated with multiple risk factors including viral infections (hepatitis B virus/hepatitis C virus/cytomegalovirus, HIV, and recently severe acute respiratory syndrome coronavirus 2) and vaccines. Though immune mechanisms have been proposed to explain the pathogenesis of acute ITP, autoimmunity with the coronavirus disease 2019 (COVID-19) vaccine is still unclear and needs further research. We report a case of acute ITP after administration of the Pfizer-BioNTech mRNA COVID-19 vaccine in a patient with previously stable ITP.