A 4.5 year old, 11.3kg, female spayed, mixed breed dog was referred to the Cornell University Hospital for Animals for evaluation of respiratory distress. Thoracic radiographs revealed pleural effusion and consolidation in the region of the right middle lung lobe. A CT scan revealed pleural effusion surrounding an enlarged right middle lung lobe with a vesicular gas pattern that did not contrast enhance. The right middle lobar bronchus ended abruptly distal to the right mainstem bronchus. These findings were characteristic of a right middle lung lobe torsion. The patient underwent a right intercostal thoracotomy and a right middle lung lobectomy. No additional thoracic pathology was identified. The patient recovered well from surgery and was discharged 2 days later.