Hypereosinophilic syndrome (HES) is an infiltrative disease of eosinophils affecting multiple organs, including the lung. Hypereosinophilic syndrome differs from acute and chronic eosinophilic pneumonia clinically and usually necessitates treatment with alkylating agents and/or corticosteroids. We describe two patients with HES and pulmonary involvement. One of our patients developed the adult respiratory distress syndrome thought to be a complication of the HES. Aggressive treatment of HES in both cases combined with intensive support in the patient with ARDS resulted in prolonged survival.