Idiopathic hypereosinophilic syndrome (HES) is a disorder characterized by the sustained overproduction of eosinophils and multiple organ damage. Rheumatologic manifestations of HES are infrequent, but persistent eosinophilia is observed in approximately 10% to 40% of patients with rheumatoid arthritis (RA). This finding may be a result of the RA itself and is often associated with active disease and the presence of extraarticular features. We describe the case of a 48-year-old man affected by HES who subsequently developed RA. Both HES and RA responded rapidly to the corticosteroid and methotrexate therapy. In this patient, the initiation of RA and HES was related, suggesting a common pathogenetic link between these two diseases.