ABSTRACTThis paper describes the clinical and radiological features of spontaneous pneumomediastinum in three racing Greyhounds. The clinical signs were characterized by dyspnoea, subcutaneous emphysema and increased bronchial tones. The diagnosis was confirmed by thoracic radiographs. The major structures of the anterior mediastinum which are normally not visible in thoracic radiographs, are easily seen with the presence of large quantities of air in the mediastinum. No definite cause of pneumomediastinum was found in these dogs but all of them recovered after 5 days' kennel confinement and a 4 week break from training.