A prospective study was set up in a busy teaching hospital to evaluate the role of a 24 h emergency ultrasonography service in patients presenting with acute abdominal pain. Seventy-five patients due for admission via the accident and emergency department with acute onset of upper or lower abdominal pain were imaged at the request of our surgical colleagues. In 14 patients (18.7%), a diagnosis was made up by sonographic examination which had not been clinically expected. Twelve of this group were female with gynaecological pathology and all 14 had their proposed emergency surgery deferred following the sonographic examination. In 26 patients (34.7%), sonography confirmed the first diagnosis suspected clinically and in nine cases (12%) confirmed the second or third differential diagnosis. Sonography made no contribution to the diagnosis in 24 patients (32%) and in two cases (2.6%) was considered misleading. The results of this study demonstrate that emergency ultrasonography is most useful in the diagnosis of female patients presenting with mid to lower abdominal pain.