The use of radiological studies as diagnostic tools in patients with suspected acute appendicitis has increased recently. In this setting, abdominal ultrasonography is viewed as a possible means of avoiding unnecessary surgery. This retrospective study of patients who underwent laparotomy for suspected acute appendicitis was undertaken to determine the sensitivity and specificity of ultrasound in diagnosing acute appendicitis and the frequency of leucocytosis in patients in whom the diagnosis was confirmed by histology. The ultrasound and surgery registers were reviewed to identify 254 referrals for abdominal ultrasound between January 2001 and December 2002 because of a clinical suspicion of acute appendicitis. Of these cases, 223 did not proceed to surgery. The study sample comprised 31 patients who had appendectomies after abdominal ultrasonography. The ultrasound reports, pathological diagnoses and white blood cell counts of these patients were obtained and formed the basis for the analysis. A histological diagnosis was available for 30 cases, in 17 of whom appendicitis was confirmed. In these patients, positive ultrasound and leucocytosis were present in five (29%) and nine (53%) respectively. Ultrasound showed 92% specificity and 29% sensitivity for the preoperative diagnosis of appendicitis. The positive predictive value of ultrasonography (83%) was higher than that of leucocytosis (69%). The sensitivity and specificity of ultrasound and leucocytosis in this study indicate limited utility as preoperative diagnostic tools.