The accuracy of ultrasonography (US) in detecting abdominal lesions and free fluid collections in patients with blunt abdominal trauma was evaluated in 250 patients. Particular attention was paid to the role of associated US-guided paracentesis in doubtful cases and in those referred for nonsurgical therapy. The overall sensitivity of US in detecting free fluid collection was 98% (51 of 52 cases) with a specificity of 99% and a positive predictive value of 100%. The overall sensitivity was 93% in spleen injuries, 80% in liver injuries, and 100% in kidney lesions with a positive predictive value of 93%, 100%, and 100%, and a specificity of 99%, 100%, and 100%, respectively. Three stable patients underwent celiotomy on the basis of the results of US-guided paracentesis. The versatility, sensitivity and, repeatability of US, along with its feasibility at bedside and the possibility of performing a guided paracentesis represent the main characteristics that make US the first diagnostic approach to patients with blunt abdominal trauma.