The authors report on two cases of congenital thrombopenia with radial aplasia. Both children display several birth defects and a mild thrombopenia; hemorragic manifestations occured in the first case only. Megakaryoblastic to platelets series, as studied with electronic microscopy, show small-sized, "microcytic" and hypogranular megakaryocytes, displaying a maturative disorder (dysmegakaryocytopoiesis). In functional studies, platelets of the first patient show an imperfect nucleotidic release and do not agregate normally with ristocetin. The second case exhibits mostly a PF3 reduction. The variety of expression of the megakaryocytic-platelets disorders appears likewise in the skeletal and visceral malformations. The whole disorder could be ascribed to a pleiotropic abnormal gene with a variable expressivity.