Lesions of the diaphragm are uncommon but important complications of blunt thoraco-abdominal traumas. Their incidence is increasing over the last decades as a consequence of the increase of the road traumatology. Preoperative diagnosis is often difficult especially when the diaphragmatic lesion is associated with other skeletal or visceral injuries that may mask the clinical or radiological signs. The Authors report 12 cases of traumatic lesions of the diaphragm due to blunt trauma observed from 1980 to 1997 and that underwent surgery. In particular they discuss about the importance of an early diagnosis and a correct surgical approach to reduce morbidity and mortality. Nine patients were operated by laparotomy; thoracotomy was performed in one case and the combined approach in the last two patients.