Seven hundred ninety consecutively seen children who had not undergone peritoneal lavage underwent imaging with computed tomography (CT) after blunt trauma. Collections of peritoneal fluid were prospectively characterized as small (51 children), moderate (32 children), or large (40 children). Associated injuries included hepatic or splenic injury in 74%, isolated renal or pancreatic injury in 5%, isolated pelvic fracture in 5%, isolated hollow viscus injury in 5%, and a combination of the above in 7%. Peritoneal fluid was the only CT abnormality in three children. A significant correlation was found between presence and increasing size of peritoneal fluid collections and clinical signs of hemodynamic instability such as lower trauma score (P = .0008 by analysis of variance), the presence of arterial hypotension (P = .0001 by chi 2 test), and hematocrit less than 30% (0.30) (P = .0001 by chi 2 test). Additionally, the presence and amount of peritoneal fluid correlated with need for laparotomy and with mortality (P = .0001 by chi 2 test for both).