A patient admitted to hospital for a supraclavicular painful mass. Ultrasonography showed soliter lymphadenopathy. He underwent H1N1 vaccination 1 week before this lymphadenopathy developed. Groosly the mass measured 1 cm × 0.8 cm × 0.8 cm. It was round, yellow to brown, slightly soft. In pathologic examination, we detected edema in capsule of lymph node. The basic architecture was preserved. There was mottled appearance caused by marked proliferation of immunoblasts which were positive with CD 30. Also large, unusual immunoblasts which closely resemble mononuclear hodgkin cells were present. These unusual immunoblasts were positive with CD 30, too. For differential diagnosis, at first we should regard hodgkin lymphoma. We suggested that lymphadenitis may be a side effect of H1N1 vaccination. © 2009 Elsevier Ltd. All rights reserved.