Records of 100 consecutive patients treated in 1973 through 1977 with post traumatic retroperitoneal hematomas (RH) were studied. Eighty RH followed blunt injury and 20 were due to penetrating trauma. Overall mortality was 26%. The worst prognosis was associated with RH from automobile accidents and pedestrian injuries. Pelvic RH were almost uniformly associated with pelvic fracture and were the primary cause of 39% of deaths. Blunt perinephric RH required renal exploration in 47% of patients. Blunt RH in other locations were associated with major visceral or vascular injury in half the patients and were the cause of death in five. Sixty-five per cent of RH due to penetrating trauma had visceral or vascular injury requiring operative correction. Contained rupture of descending thoracic aorta presented as retrogastric RH in two patients. RH from penetrating trauma should be explored routinely, since 65% are associated with visceral or vascular injury.