Of our last 2483 renal trauma patients, 113 had grade IV injuries. In most the mechanism was a penetrating injury (60%: 30% gunshot, 30% stab wounds). Associated injuries were common (80%) and hospital stays prolonged, averaging 16 days. Most of the patients (70%) required transfusion, some massively (average volume 4.4 liters, range 0-30 liters). Surprisingly, not all patients with grade IV renal injuries had gross hematuria: 25% had microhematuria, and 4% had neither microscopic nor gross hematuria. Computed tomography (CT) diagnosed the injury correctly in 100% of the patients in whom it was performed; when CT was not available, "one-shot" intraoperative intravenous pyelography (IVP) demonstrated grossly abnormal findings in 90%. Renal exploration was performed in 78%, resulting in 69% renorrhaphy and 9% nephrectomy rates in our 113 patients. Almost all those with penetrating trauma required exploration (97%), whereas only 50% of those with blunt trauma did so. The overall complication rate and kidney-specific complication rate did not differ significantly between patients who were observed and those who underwent surgery. Complications rates were similar in grade IV renal laceration patients and grade III patients. Delayed complications after hospital discharge were not seen, although follow-up was rare in this inner-city trauma population. Among the 21% of patients in whom postoperative nucleotide renal function scans were available, function was generally good (average 36%). Only patients who underwent concomitant vascular repair had poor function (below 20%).