Blunt trauma patients with pelvic fractures have been shown to have a two-fold to five-fold increased risk of aortic rupture compared with the overall blunt trauma population. A retrospective review was performed to determine whether the relationship between aortic rupture and pelvic fracture could be further delineated using a pelvic fracture classification based on mechanism of injury. Of 4157 consecutive blunt trauma patients, 371 (8.9%) had pelvic fractures, 34 (0.8%) had ruptured thoracic aortas and 12 had both injuries. When pelvic fractures were classified according to vector of force, 10 of 12 (83%) aortic ruptures occurred in patients with an anterior-posterior compression fracture pattern, an incidence of aortic rupture eight times greater than that of the overall blunt trauma population. There was no increased incidence of aortic rupture among patients with any other pelvic fracture pattern. We conclude that the previously reported association between aortic rupture and pelvic fracture can be further specified to include, predominantly, those patients with an anterior-posterior compression fracture pattern.