Inherited thrombocytopenias are rare, heterogenous and probably under-diagnosed because often classified as autoimmune thrombocytopenia. About 20 genes were described responsible for these thrombocytopenias. Precise diagnosis is necessary because the prognosis is different and some of them can evolve into hemopathies. First of all, it is important to gather a body of evidence to orientate towards an inherited cause: presence of the thrombocytopenia since childhood and of other family cases is a strong argument. Secondly, it is difficult to target the genetic investigations that settle the precise diagnosis. Genetic variants responsible for inherited thrombocytopenias affect different stage during megakaryocytopoiesis and cause thrombocytopenias with distinct characteristics. Presence of extra-hematological features, platelets' size measurement and evaluation of bone marrow megakaryocyte morphology when it is possible allow a primary orientation. We propose a diagnostic approach considering extra-hematological features, mode of inheritance, morphology, molecular and functional platelets' studies and bone marrow megakaryocyte morphology in order to better target genetic study. Nevertheless, despite this approach, some inherited thrombocytopenias remain still unexplained and could benefit from new methods of new generation sequencing in the future.