The objective of this prospective study was to determine the sensitivity, specificity, and accuracy of the rapid trauma ultrasound examination, performed by emergency physicians, for detecting free peritoneal and thoracic fluid in patients presenting to a level I trauma center with major blunt or penetrating torso trauma. Emergency medicine residents and faculty were trained to perform an ultrasound examination of the torso evaluating for free intraperitoneal, retroperitoneal, pleural, and pericardial fluid. In the 245 study patients, emergency physicians examined 975 intracavitary spaces and demonstrated 64 positive findings for free fluid as documented by computed tomography scan, diagnostic peritoneal lavage, exploratory laparotomy, chest radiography, tube thoracostomy, or formal two-dimensional echocardiography. The rapid trauma ultrasound examination was 90% sensitive, 99% specific, and 99% accurate. Ultrasonography can serve as an accurate diagnostic adjunct in detecting free peritoneal and thoracic fluid in trauma patients. Appropriately trained emergency physicians can accurately perform and interpret these trauma ultrasound examinations.