Diagnostic modalities in abdominal trauma. Peritoneal lavage, ultrasonography, computed tomography scanning, and arteriography. Numerous algorithms encompassing the diagnostic studies described above have been published in recent years. For practical purposes, diagnostic peritoneal lavage and CT scanning are the diagnostic studies most commonly used in patients without obvious indications for celiotomy after blunt or penetrating abdominal trauma. Diagnostic peritoneal lavage is invasive, rapidly performed, cheap, and accurate and has a primary role in documenting intra-abdominal bleeding or contamination in hypotensive patients with blunt trauma or selected stable patients with penetrating stab wounds. It misses small and large injuries to the diaphragm and cannot rule out injury to retroperitoneal structures. Computed tomography is noninvasive, time consuming to perform, expensive, and accurate and has a primary role in defining the location and magnitude of intra-abdominal injuries in stable patients with blunt trauma or with penetrating trauma to the flank or back. In many hospitals, it misses gastrointestinal perforations or ruptures. Both studies may be needed in the same stable patient, and both should be available and used in a complementary fashion in the modern trauma center. 