The CT scans of 25 children with blunt renal and ureteral trauma were analyzed to determine the severity of injury, the appearance of retroperitoneal fluid collections, and whether the extent of these collections correlated with the severity of injury. CT showed renal parenchymal injuries in 23 patients and ureteral injuries in two patients. Retroperitoneal fluid was detected in 19 (76%) of 25 patients. Perirenal fluid collections were present in all 19, periureteral fluid in 12, interfascial fluid in eight, anterior pararenal fluid in four, and psoas hemorrhage in three. The presence of perirenal and periureteral fluid was not a good predictor of the extent of renal injury. Fluid collections in the interfascial or anterior pararenal spaces and psoas muscle appeared to correlate with the severity of injury. Patients with these fluid patterns usually had renal fractures, arterial injuries, or ureteral disruptions. The presence of perirenal and periureteral fluid did not correlate with the extent of renal injury, while the presence of interfascial, anterior pararenal, and psoas muscle fluid correlated somewhat with renal fractures and renal pedicle disruption.