Ultrasound diagnostic imaging has been demonstrated to be a valuable investigative tool in the evaluation of trauma patients in Europe and Japan. In the United States, however, ultrasound has not been widely used by trauma surgeons because of its lack of availability in the trauma resuscitation area and the associated cost and lack of full-time availability of a technician. In this prospective study, four attending trauma surgeons, four trauma fellows (PGY 6 and 7), and 25 surgical residents (PGY 4) at a level I trauma center were trained in specific ultrasound techniques to identify fluid in trauma patients with thoracoabdominal injuries. Their ultrasound evaluations of 476 patients demonstrated that in 90 patients with clinically significant injuries, ultrasound imaging successfully detected injury in 71, for a 79% sensitivity. Specificity was 95.6%. We conclude that (1) surgeons can rapidly and accurately perform and interpret ultrasound examinations; and (2) ultrasound is a rapid, sensitive, specific diagnostic modality for detecting intraabdominal fluid and pericardial effusion.