OBJECTIVE To assess the sensitivity, specificity, and predictive value of ultrasonography in patients with blunt abdominal or thoracic trauma in regard to the indication for immediate operation, delayed abdominal exploration, or conservative treatment. METHODS A retrospective study was conducted after consecutive sampling of 1151 patients in a nonrandomized control trial. METHODS The study was conducted at the University Hospital of Innsbruck (Austria), which serves as a general community hospital and a major primary care and referral center. METHODS All patients with blunt abdominal or thoracic trauma with or without polytraumatization were eligible for the study; a total of 1151 patients were observed from 1980 to 1990. According to the ultrasonographic findings, patients were divided into three groups: immediate operation, primary conservative treatment, and conservative treatment (normal ultrasonographic findings). Ultrasonography was repeated when the clinical findings or laboratory test results showed the development of intra-abdominal hemorrhage or signs of organ laceration. METHODS Ultrasonography in the emergency department or intensive care unit. METHODS Conservative or operative treatment based on ultrasonographic and clinical findings. RESULTS Ultrasonography showed a sensitivity of 99%, a specificity of 98%, a positive predictive value of 0.97, and a negative predictive value of 0.99 in regard to the indication for surgery in cases of blunt abdominal or thoracic trauma. Ultrasonography is not reliable in patients with intestinal perforation and large retroperitoneal hematomas. CONCLUSIONS Ultrasonography saves time and money, can be performed in the emergency department, shows high sensitivity and specificity, and is the method of first choice in the evaluation of blunt trauma.