Immune thrombocytopenic purpura is rarely seen in Hodgkin disease and the presence of platelet-associated antibody has not been previously reported in these patients. A patient with Hodgkin disease is described who developed a destructive thrombocytopenia demonstrated by shortened platelet survival. In conjunction with his thrombocytopenia, he had marked elevation of platelet-associated immunoglobulin G levels (nanograms IgG per 10(9) platelets: 15,187 prior to splenectomy and 71,130 and 81,900 after surgery). Mean values (+/-SD) of control subjects averaged 1,975 + 381 and four patients with Hodgkin disease and normal platelet counts had levels ranging from 1,581 to 4,011. We suggest that this patient had immune-mediated thrombocytopenia; whether the increase in platelet-associated immunoglobulin G was due to antiplatelet antibody or to adsorbed or phagocytosed immune complexes cannot be demonstrated by these studies. The platelet-associated immunoglobulin G test may be useful in evaluating these patients.