Over the past 30 years, thrombopoietin has moved from myth to logic, from an “activity” (platelet formation) that many believed did not reside in a unique molecule, to its cloning, biological and structural characterization, to its role in normal and neoplastic hematopoiesis, and to its widespread use to treat several life-threatening conditions including severe aplastic anemia or thrombocytopenia due to autoimmunity, chemotherapy-related toxicity and liver failure. This evidence concerns the gene THPO and aplastic anemia.