The objective of this study was to evaluate the diagnostic yield of multislice CT using a radiation dose equivalent to that of conventional abdominal x-ray (KUB). One hundred forty-two patients were prospectively examined with ultrasound and a radically dose-reduced CT protocol (120 kV, 6.9 eff. mAs). Number and size of calculi, presence of urinary obstruction, and alternative diagnoses were recorded and confirmed by stone removal/discharge or by clinical and imaging follow-up. The mean effective whole-body dose was 0.5 mSv in men and 0.7 mSv in women. The sensitivity and specificity in detecting patients with calculi was 97% and 95% for CT and 67% and 90% for ultrasound. Urinary obstruction was similarly assessed, whereas CT identified significantly more alternative diagnoses than ultrasound (P<0.001). With regard to published data for standard-dose CT, the present CT protocol seems to be comparable in its diagnostic yield in assessing patients with calculi, and its radiation dose is equivalent to that of KUB.