PURPOSE: To assess the diagnostic accuracy and clinical efficacy of noncontrast spiral CT in patients withsuspected acute appendicitis. MATERIALS AND METHODS: Over a six-month period, 100 patients with suspected acuteappendicitis were prospectively evaluated with noncontrast spiral CT. All scans were obtained from the lower bodyof L3 to the symphysis pubis, with 5mm or 10mm collimation and pitich of 1 or 1.5, and without intravenous or oralcontrast material. Diagnosis was established by means of surgical or clinical follow-up. Prospective diagnosisbased on CT findings was compared with surgical results and clinical follow-up. RESULTS: Acute appendicitis wasconfirmed in 47 of 100 patients. On the basis of the basis of the CT findings, SI patients were prospectivelyinterpreted as positive for appendicitis, but in six the diagnosis was false-positive. Two of the 47 with acuteappendicitis were prospectively interpreted as normal. The preoperative diagnosis of acute appendicitis was, thus,45 true-positive, 47 true-negative, six falsepositive and two false-negative, yielding a sensitivity of 96%, aspecificity of 89%, an accurace of 92%, a positive predictive value of 88%, and a negative predictive value of96%. Using CT, an alternative diagnosis was established in 14 patients. CONCLUSION: Noncontrast spiral CT is auseful technique for diagnosing acute appendicitis.