Idiopathic hypereosinophilic syndrome (HES) is a rare, chronic hematological disease mainly characterized by unexplained prolonged eosinophilia, with frequent evidence of secondary organ damage. Treatment with steroids, chemotherapy, interferon-alpha (IFN-alpha), or imatinib-mesylate may improve the prognosis. Here we describe the case of a young male patient with a six-year history of HES and severe heart involvement who, after unsuccessful treatment attempts with steroids, hydroxyurea and IFN-alpha, had a prompt, clinical and hematological complete remission following administration of imatinib. As his cardiac function also markedly improved, he was considered for heart transplant. However, seven years after the onset of the disease and four months after the termination of imatinib treatment the patient died of a cerebral hemorrhage that occurred during an episode of acute respiratory sepsis. Imatinib has been previously reported to be effective in some hematological conditions with no evidence of the BCR/ABL transcript. The mechanisms that are probably involved in the response to imatinib in HES are also discussed.