Hypereosinophilia can be related to various diseases; when it occurs without an obvious cause it is called idiopathic hypereosinophilic syndrome (IHES). We describe a patient with increasing eosinophilia, which in spite of extensive diagnostic procedures initially remained unexplained. However, during follow-up it became apparent that this patient had a lethal enteropathy-associated T lymphoma (EATL) causing the hypereosinophilia.