A 32-year-old man who had previously undergone chemotherapy for testicular seminoma 11 years ago was admitted to our hospital with a pain in the right leg. Computed tomography (CT) and bone scintigraphy revealed splenomegaly and multiple bone disease. Laboratory examination showed thrombocytopenia. The pathologic diagnosis of the resected spleen and the biopsied rib was angiosarcoma. We found no reports of angiosarcoma following previous chemotherapy for testicular cancer. It is unclear whether the angiosarcoma is a secondary neoplasm induced by the chemotherapy or not. However, the patient had a chromosomal aberration of the peripheral lymphocytes. The chemotherapy might also have affected the chromosomal aberration presumably in endothelial progenitor cells causing the development of a secondary neoplasm. To our knowledge, this is the first case of angiosarcoma after chemotherapy for testicular seminoma.