Idiopathic hypereosinophilic syndrome (IHES) is a rare disease that is characterized by otherwise unexplained persistent eosinophilia and organ damage caused by eosinophilic infiltration. Its manifestations are highly variable but clinically apparent arthritis is uncommonly observed. Although Korean cases of severe eosinophilia in patients with rheumatoid arthritis (RA) or IHES concurrent with RA have been published, there are no reports of IHES with joint involvement. This paper reports a case of IHES presenting with persistent peripheral eosinophilia, fever, skin rash, multiple lymphadenopathy, and polyarthritis, including the distal interphalangeal joints of the hands. (J Rheum Dis 2018;25:207-211)