This report describes a case of pyothorax in an 11 month old, male castrated domestic short hair cat. The cat was referred for further evaluation of acute dyspnea, pleural effusion, and the radiographic finding of an intrathoracic metallic foreign body. Right sided thoracotomy was performed and the metallic foreign body, a sewing needle, removed. Aggressive medical treatment of the cat involved closed chest drainage and lavage, systemic antibiotic therapy, and supplemental oxygen therapy. Despite appropriate treatment, the cat did not improve clinically, and eventually required a right pneumonectomy. This report will discuss the relevant aspects of this case and provide an overview of the occurrence, etiology, diagnosis, and treatment of pyothorax in cats.