A two-year-old male intact Beagle was presented to the Cornell University Hospital for Animals for evaluation of progressing dyspnea and lethargy. Thoracic radiographs, ultrasound, thoracocentesis, cytology and CT were suggestive of a pyothorax involving both pleural cavities. A median sternotomy and thoracic exploratory surgery were performed to debride abnormal tissues and flush the pleural cavity. The patient was managed postoperatively with clindamycin, enrofloxacin, and a thoracostomy tube. Though the underlying cause of the pyothorax was not detected in any of the diagnostics, bacterial isolates Fusobacterium spp., Bacteroides spp., and Prevotella spp. were isolated in fluid cultures. The patient’s condition improved post-operatively and he continued to do well when assessed at his two week recheck appointment.