Quantitative peritoneal lavage was performed in 52 children with blunt abdominal trauma to determine the presence of intraabdominal injuries. A strongly positive lavage was 100% accurate in diagnosing an intraabdominal injury requiring operation. A negative lavage demonstrated absence of a significant intraperitoneal injury with 100% accuracy. A weakly positive lavage was not diagnostic and required additional evaluation including intravenous pyelography echography, and arteriography. Diagnosis and treatment was prompt, and in 20 of 21 cases, operation was performed within 4 hr. Peritoneal lavage was found to be safe and much more accurate than physical examination in diagnosing significant intraabdominal injury.