A 50-year-old man was admitted to our hospital because of intracranial hemorrhage and thrombocytopenia (platelet count: 3,000/microliter). Low levels of IgG (76 mg/dl) and IgA (30 mg/dl) and a normal pattern of peripheral blood T and B cell subsets yielded a diagnosis of common variable immunodeficiency (CVID). The number of megakaryocytes in bone marrow was within normal limits (64/microliter), and a diagnosis of idiopathic thrombocytopenic purpura was made. Both high-dose intravenous gamma-globulin and prednisolone were ineffective. Because of the coexistence of CVID, splenic irradiation (total 15 Gy) was performed instead of splenectomy. The platelet number began to increase 5 days after the initiation of irradiation, had increased to 8.7 x 10(4)/microliter at the end of irradiation, and was 22.9 x 10(4)/microliter 2 weeks later.