Between July 1989 and June 1991, 312 patients with blunt thoracic or abdominal injuries were examined prospectively. Sonographic examination was performed by surgeons in the emergency room using a mobile ultrasound unit. In 113 (36.2%) cases pathologic findings were demonstrated sonographically. These included 47 cases of hemothorax, 11 pericardial effusions, 52 cases of intra-abdominal fluid, 24 lesions of intra-abdominal organs, and 10 cases of retroperitoneal hematoma. Physical examination findings were positive in 96 (30.8%), negative in 63 (20.2%), and equivocal in 153 (49.0%). Two hundred thirty-nine patients had between one and eight injuries in addition to the blunt abdominal or thoracic trauma. These patients had an average Injury Severity Score (ISS) of 19.9 (range, 1 to 75). The 73 patients with isolated blunt trauma of the thorax or abdomen had an ISS of 4.9 (range, 0-25). None of the 66 patients (21.2%) with positive clinical findings and negative sonographic examination results had to be operated on later in the course of treatment, while 5 (36%) of 14 patients (4.5%) with negative physical examination findings and positive sonographic findings had to undergo surgery. The sensitivity for the demonstration of intra-abdominal fluid and organ lesions was 98.1% and 41.4%, respectively. The overall sensitivity and specificity of the ultrasonic examination were 90.0% and 99.5%, respectively.