A 3.5 year old, castrated male Rottweiler mix-breed dog presented to the Small Animal Internal Medicine Service at Cornell University Hospital for Animals on 9/29/2009 for evaluation of a cough and potential lung masses. The dog had a one month history of occasional diarrhea, inappetence and a cough that was unresponsive to amoxicillin with clavulanic acid. Radiographs taken at the referring veterinarian revealed discrete soft tissue opacities throughout the lung fields. Diagnostics performed on 9/29/09 included a Complete Blood Count and Chemistry Panel, fecal flotation, a thoracic and abdominal CT-scan, ultrasound-guided aspiration of lung and liver, an echocardiogram, and an endotracheal wash. Results of the aspirates and endotracheal wash revealed severe eosinophilic infiltration of the liver and lungs leading to a diagnosis of canine idiopathic hypereosinophilic syndrome. Prednisolone, amoxicillin with clavulanic acid and Fenbendazole were administered. The patient initially responded well to treatment but was euthanized two weeks later due to complications from gastrointestinal perforations.