Injuries missed at initial operation have the potential to cause the most disastrous complications in trauma patients. Over the past 5 years, 12 patients have required re-operation for 14 injuries missed at initial laporatomy and/or thoracotomy. Six missed injuries were vascular, two each in the thorax, pelvis, and retroperitoneum. The other eight were visceral: three small bowel (one patient), two pancreatic, and one each of the heart, ureter, and diaphragm. Five patients (42%) died, three with missed vascular and two with missed visceral injuries. Three died due to complications directly related to their missed injuries, while the unrecognized injury did not play a significant role in the other two. Indications for re-operation in patients with vascular injuries were hypotension in two patients, persistent output from drains in three, and refractory acidosis in one. Re-exploration in visceral injuries was for clinical sepsis in three patients, DIC in one, cardiac tamponade in one, and persistent chest tube drainage in one. Eleven of the 12 patients presented to the E.D. in shock. All patients had multiple injuries with a mean of 3.25 organ systems injured. Hypotension, coagulopathy, and/or hypothermia (T < 92$dG) were felt to have contributed to missing the injury in five of the patients with vascular, and three of the patients with visceral injuries. In the four other patients, injuries were missed due to inadequate exploration or a low index of suspicion in the presence of multiple injuries. Mean time to re-exploration was significantly less in survivors for both vascular (4.4 vs. 11.2 hr) and visceral injuries (4.3 vs. 9 days). In nonsurvivors, the delays in re-exploration were due to incorrectly ascribing blood loss to coagulopathy in four and intra-abdominal sepsis to pneumonia in one. Missed injuries, although rare following surgical exploration for serious trauma, result in preventable morbidity and mortality. Patients with clinical indications of ongoing bleeding should be re-explored within 4 hours, and those with clinical sepsis or early multiple organ failure should undergo abdominal re-exploration within 4 days to detect undiagnosed injuries.