The ultrastructural pathology of GATA-1, V205M and G208S macrothrombocytes was discussed in earlier investigations. This study has used the same technology to evaluate macrothrombocytes from a patient with the GATA-1, R216Q mutation. Some of the pathological features observed in macrothrombocytes from patients with the V205M and G208S variations including hypo- and agranular platelets, tubular inclusions and platelets within platelets, as well as platelets within platelets within platelets were identified. However, tubular membrane sheets in megakaryocytes and platelets of the V205M and G208S types and large groups of platelets attached to platelets to form megathrombocytes were not observed. The unique pathology of the megathrombocytes from this patient was the near absence of dense bodies in his giant cells. Storage Pool Deficiency, together with large platelets, defective adhesion and aggregation of his macrocytes under shear stress to vWF and collagen and defective clot retraction may contribute to the pathogenesis of his bleeding disorder.