This paper has attempted to summarize the more common disease entities which may be accompanied by or may lead to a disorder of hemostasis and/or thrombosis. It is to be emphasized that the vascular component of hemostasis is often overlooked by clinicians caring for individuals with disorders in hemostasis and thrombosis. It is hoped that this brief summary will alert clinicians that the vasculature is equal in importance to the coagulation protein system and to platelets in leading to a hemorrhagic or thrombotic diathesis.