Between 1975 and 1990, 85 patients with diaphragmatic rupture following blunt trauma were treated at the Royal Brisbane and Princess Alexandra Hospitals, Brisbane. There were 65 on the left, 17 on the right and three were bilateral. Road trauma was the cause in 88% of cases. In the first 48 h the diagnosis was made by chest X-ray in 51 patients, laparotomy in 22, autopsy in two, emergency room thoracotomy, ultrasound and pneumoperitoneum each in a single patient. Seven patients (8%) had delay in diagnosis greater than 48 h ranging from 6 days to 6 months. Diagnosis was subsequently made by pneumoperitoneum (3), chest X-ray (1) and exploratory thoracotomy (1). Two patients presented with a strangulated diaphragmatic hernia 3 and 6 months following an acute admission with blunt chest trauma and urological trauma respectively. During the study period a further five patients presented with an obstructing diaphragmatic hernia. Sixteen patients died (19%), fifteen from associated injuries and one related to the diaphragmatic repair. Ruptured diaphragm should be suspected in patients with severe chest trauma, particularly those requiring positive pressure ventilation, patients with intra-abdominal injuries and those with pelvic fractures. Early recognition and repair results in low morbidity and mortality. Measures that confirmed the diagnosis in patients with delay included repeated chest X-rays and pneumoperitoneum.