Germ line mutations in ETV6 are responsible for a familial thrombocytopenia and leukemia predisposition syndrome. Thrombocytopenia is almost completely penetrant and is usually mild. Leukemia is reported in ∼30% of carriers and is most often B-cell acute lymphoblastic leukemia. The mechanisms by which ETV6 dysfunction promotes thrombocytopenia and leukemia remain unclear. Care for individuals with ETV6-related thrombocytopenia and leukemia predisposition includes genetic counseling, treatment or prevention of excessive bleeding and surveillance for the development of hematologic malignancy.