Hypereosinophilic syndrome (HES), a rare systemic disease, was first described in 1968. As a subtype of HES, idiopathic hypereosinophilic syndrome (IHES) is defined as hypereosinophilia of unknown cause, excluding tumor, infection, allergy, and immune system disease. In most cases, more than 1 organ is affected in patients with IHES. [1] The first-line drug for the treatment of IHES is glucocorticoid, which is effective for both hypereosinophilia and clinical manifestations. [2] However, when the outcome of hormone treatment is unsatisfactory, immunosuppressive or antineoplastic agents can also be administered. [3] Due to the low incidence of IHES, there is currently a lack of large-scale retrospective studies of the disease. We aimed to identify factors predictive of prognosis and determine the endpoint eosinophil (EOS) count after pharmacological therapy and the time at which a change of therapy should be considered following the failure of hormone treatment.Rui Tang and Shubin Lei contributed equally to this work.