Budd-Chiari syndrome (BCS) is characterized by hepatic venous outflow obstruction, which sometimes may be life threatening, with the development of fulminant hepatic failure. In cases of this kind, the most frequent underlying cause of BCS, myeloproliferative neoplasms (MPN), should always be excluded first, and molecular analysis of the Janus Kinase 2 (JAK2) mutation must always be performed [1]. While the association of BCS with polycythemia vera, essential thrombocythemia, and idiopathic myelofibrosis is well documented, hypereosinophilia has only been described in sporadic cases [2–7]. Furthermore, Jak2 mutation in association with hypereosinophilia has been reported very rarely and its prevalence in this disorder still requires further investigation [8,9]. To the best of our knowledge, cases with the above association occurring together with BCS have not been reported until now. Here, we describe a young woman presenting with idiopathic eosinophilia, JAK2 mutation, and BCS. We also elaborate briefly on the biological mechanism and clinical features of this rare entity. In our opinion, this case supports the formal inclusion of hypereosinophilic syndrome (HES) in the WHO MPN category and also raises the possible pathogenetic contribution of eosinophils, or their products, in MPN-associated splanchnic vein thrombosis.