A prospective study was carried out to compare the value of ultrasound examination with conventional management in patients presenting with emergency surgical problems. During an 4 years period the authors followed 301 patients referred to the Ist Institute of Surgery of the University of Rome "La Sapienza". After immediate clinical evaluation one or more US examinations were performed in each patient following a standard protocol of study. Abdominal emergencies were the most frequent conditions, found in 75% of the cases and the acute abdomen due to trauma in 17.6% of the cases. The overall sensibility, specificity and accuracy of clinical examinations and US examinations were respectively of 88%, 33%, 70% and 95%, 94%, 95%. In 38 patients (12.7%), a diagnosis was made up by sonographic examination which had not been clinically expected (group A). The principal condition in this group was gynaecological pathology, found in 17 patients. In 161 patients (53.3%) sonography confirmed the first diagnosis clinically suspected (group B) and in 23 cases the second or third differential diagnosis (group D). Sonography made no contribution to the diagnosis in 77 cases (25,5%) and only in 2 cases was considered misleading. The result of this study demonstrate the usefulness of emergency ultrasonography in gynecological, gall bladder, pancreatic and vascular diseases. Moreover sonography must be considered the principal diagnostic tool in patients with trauma. In order to recognize gynecological diseases which can simulate appendicitis US examination must be considered necessary in young female patients. When appendicitis is suspected US is useful in children and in older patients too.