OBJECTIVE To analyse our cases of acute rupture of the diaphragm after blunt trauma to find out how to diagnose it earlier and manage it more promptly in future. METHODS Retrospective study of casenotes. METHODS Division of general surgery, district hospital, Taiwan. METHODS 50 Patients who presented with acute rupture of the diaphragm after blunt trauma during the 10 year period 1982-91. METHODS Morbidity and mortality. RESULTS The left hemidiaphragm was injured in 43 cases (86%), and the right in 7 (14%). The most common cause was road traffic accidents. 48 Patients had associated injuries, mainly to the chest and abdomen, and pelvic fractures. 44 Ruptured diaphragms were diagnosed before operation by chest radiography or upper gastrointestinal contrast examination. The transabdominal approach was the most appropriate, because 23 patients had intra-abdominal visceral injuries as well. 20 Patients (40%) had complications, and the rate was 33% among those treated within 24 hours and 70% among those whose treatment was delayed longer than 24 hours (p = 0.067). There were 3 deaths (6%); one patient died of empyema of the right chest as a result of simultaneous perforation of a hollow viscus. 6 Patients were permanently disabled by head and spinal injuries, and pelvic fractures. CONCLUSIONS The prognosis of repairing diaphragmatic hernias is good as the disability rate is low. The diagnosis should be kept in mind in all patients with chest injuries, pelvic fractures, or abdominal injuries with hypoxaemia, as this will result in earlier treatment and improve prognosis. The transabdominal approach is the most appropriate because it makes simultaneous abdominal injuries easier to treat. Correct operative management at an early stage will keep mortality to a minimum.