SummaryThis paper describes a patient with massive eosinophilic ascites as presenting manifestation probably due to idiopathic hypereosinophilic syndrome. Eosinophilic ascites and stomach wall involvement were the first detected abnormalities. The subsequent course was characterised by interstitial pulmonary disease and pleural and pericardial effusion. Grand mal epilepsy and numbness of the left arm indicated central nervous system involvement. Treatment with corticosteroids resulted in complete remission.The differential diagnosis of eosinophilic gastroenteritis and idiopathic hypereosinophilic syndrome is discussed.