Secondary causes of thrombocytopenia as immunologic thrombopenia purpura, or ITP, are far more common than inherited causes, which even as a group, are rare. Nevertheless, diagnosis is important and progress made in uncovering the molecular basis of these disorders has contributed greatly to our knowledge of these diseases. Inherited thrombocytopenias are a heterogeneous group of disorders. Different criteria have been suggested to classify the forms, such as the inheritance mechanism and the platelet volume as well as the associated platelet dysfunctions or clinical abnormality. This paper describes the clinical and biological data, and current knowledge of the molecular findings of inherited thrombocytopenia, allowing a diagnostic approach to these diseases.