A seven year old, castrated male Siberian husky mix presented with a several month history of intermittent increases in respiratory rate and effort. In the few days prior to presentation, the patient had become anorexic, lethargic, and had episodes of coughing after drinking and hemoptysis. Physical exam findings and thoracic radiographs revealed evidence of severe pneumothorax. History and diagnostic findings made spontaneous pneumothorax the primary differential. A CT scan showed a soft tissue abnormality in the thorax which was localized to the left cranial lung lobe. The patient was taken to surgery, where a torsion of the left cranial lung lobe was found and resected. Post-operatively, medical management including cage rest and bilateral thoracostomy tubes attached to continuous suction failed to prevent the recurrence of the pneumothorax. Subsequent thoracoscopy was unable to localize the cause of the pneumothorax. Post thoracoscopy, therapy was discontinued in an attempt to allow the pneumothorax to resolve on its own. The patient remained stable and repeat radiographs showed no evidence of pneumothorax. The cause of the spontaneous pneumothorax in this case was never determined.