Preoperative diagnosis of diaphragmatic rupture caused by blunt injury is often difficult because of serious concurrent injuries, a lack of specific clinical signs, and simultaneous lung disease that may mask or mimic the diagnosis radiologically. Previous reports have suggested that a preoperative diagnosis is established on the basis of chest radiographs in only one third of patients. In order to assess the value of chest radiographs and other imaging techniques in diagnosing traumatic rupture of the diaphragm, we retrospectively reviewed all preoperative diagnostic imaging performed in 50 patients with surgically proved hemidiaphragmatic rupture due to blunt trauma. Chest radiographs were diagnostic in 20 (46%) of 44 patients with left-sided rupture and were considered suspicious enough to warrant further diagnostic studies in an additional eight patients (18%). Five patients with initially normal findings on chest radiographs had diagnostic findings on delayed chest radiographs. Chest radiographs were strongly suggestive in only one (17%) of six patients with right-sided hemidiaphragmatic rupture. CT was diagnostic for diaphragmatic rupture in only one (14%) of seven instances in which it was performed. MR was diagnostic in both patients in whom it was performed. Our experience indicates that chest radiographs obtained at admission and repeated soon after are more valuable in suggesting the diagnosis of traumatic rupture of the diaphragm than previously reported, particularly in the more frequent, left-sided injuries. This increased sensitivity may be due to a greater level of suspicion maintained in a trauma referral center in which this injury is not uncommon.