For practical purposes, acquired eosinophilia can be divided into secondary, clonal, and idiopathic eosinophilia. The causes of secondary eosinophilia may be parasitic infections, allergic diseases, vasculitis, drug reactions, and lymphomas. Hypereosinophilic syndrome (HES) is a subcategory of essential eosinophilia. The diagnosis of idiopathic eosinophilia means that secondary and clonal eosinophilia have been excluded. The aim of this study was to present cases of patients with HES, showing the possible differentiation of organ involvement, which translates into various possible courses of HES. After analysing data from the literature on the clinical course of HES in our patients, we concluded that hypereosinophilic HES syndromes constitute a challenge for physicians of various specialisations. The common denominator connecting all cases will always be an increased number of eosinophilia and a good clinical response to anti-IL-5 antibody treatment.