Adult-onset Still's disease (AOSD) is a systemic inflammatory disorder with the characteristics of high spiking fever, evanescent salmon-colored skin rash, arthralgia or arthritis, lymphadenopathy, hepato-splenomegaly, sore throat, leukocytosis, negative autoantibody and hyperferritinemia. There are reports that rheumatic diseases such as dermatomyositis, polymyositis, hypertrophic osteoarthropathy, and polymyalgia rheumatica are associated with neoplasms. And small cell lung cancer, thymoma, lymphoma, leukemia, and breast cancer are known to be more associated with paraneoplastic syndromes mimicking rheumatic diseases. We experienced a case with bronchioloalveolar carcinoma who developed clinical manifestations of AOSD. Although there are several reports that AOSD is associated with paraneoplastic syndrome, to our knowledge, this is the first case of bronchioloalveolar carcinoma mimicking AOSD reported in the world.