The medical records of 12 dogs with chronic pyogranulomatous pleural disease unresponsive to medical management were reviewed retrospectively. Resection of the mediastinal pleura (mediastinectomy) was performed through a median sternotomy to remove all diseased and surgically accessible mediastinal pleural tissue. Dogs were re-examined two weeks postoperatively, and long-term outcome was evaluated by contacting owners by phone. Twelve dogs underwent mediastinectomy; additional surgeries included subtotal pericardiectomy (8), lung lobectomy (4) and partial diaphragmatic resection (2). Histology of resected tissue consistently revealed neutrophilic, pyogranulomatous cellulitis/serositis. Foreign material was evident in the mediastinal tissue of five dogs and microorganisms were recovered from three dogs. Two dogs developed pneumothorax immediately postoperatively; one dog developed haemothorax one month postoperatively and was euthanased. Median follow-up time was eight months (range: 6–43 months); eleven dogs were alive and considered to be symptom-free by their owners. Mediastinectomy resulted in complete resolution of symptoms in most dogs (92 per cent) and was associated with a low incidence of major complications. The results of this study indicated that mediastinectomy results in favourable outcome for dogs with chronic pleural pyogranulomatous pleural disease unresponsive to medical management.