The pathogenesis of hypersplenic thrombocytopenia is complex. About half of these patients have shortened platelet lifespans. A few have an expansion of the intravascular platelet space, and it is likely that there is a shift of platelets from the vascular to the splenic space in most patients. Estimates of platelet production vary from normal to about twice normal in this syndrome. There remains little need to invoke a theory of suppression of platelet production by the enlarged spleen. In fact, it may be that splenectomy results in a decrease of platelet production.