We encountered a 59-year-old man with advanced lung cancer with multiple swollen lymph nodes. At autopsy the lung cancer was revealed as giant cell carcinoma. Microscopic examination showed no cancer cells, but there was polyclonal proliferation of plasma cells in the lymph nodes and in the bone marrow. In the kidneys, proliferation of mesangial matrices and mesangial cells was found. This presentation resembled multicentric Castleman's disease (MCD), in which interleukin-6 (IL-6) has a great role. Immunohistochemical staining was positive for IL-6 in cancer cells. This is the first reported case of an IL-6-producing giant cell carcinoma of the lung with MCD-like presentation.