A women with congenital cavernous hemangiomas and a bleeding diathesis since childhood was found to have a qualitative platelet defect characterized by the absence of a second-phase aggregation induced by epinephrine, adenosine diphosphate (ADP), and collagen, accompanied by decreased levels of adenosine triphosphate (ATP) and ADP, with a high ATP-ADP ratio consistent with the diagnosis of "storage pool disease" of the platelets. There was no evidence of disseminated intravascular coagulation or circulating antiplatelet antibodies. The bleeding tendency responded to platelet transfusion.