PURPOSE: To assess the usefulness of a CT severity index(CTSI) for the evaluation of acute pancreatitis and to correlate it with clinical findings. MATERIALS AND METHODS: We retrospectively evaluated contrast enhanced CT in 34 patients with acute pancreatitis. They were categorized into low-score(0-2), middle-score(3-6), and high-score(7-10) groups according to CTSI points, and those groups were correlated with duration of fasting period, days in hospital morbidity and mortality. We attempted to determine the differences in CTSI between pancreatitis caused by alcohol and by biliary tract disease. RESULTS: Of 34 patients, 11 were placed in the low-score group, 19 in the middle-score group, and 4 in the high-score group. The patients in the middle-score group experienced longer fasting period and stayed longer in hospital than those in the low-score group(p<.05 and p=.08, respectively). Morbidity was 0% in the low-score group, 37% in the middle-score group and 50% in the high-score group. Mortality occurred in two patients in high-score group, only. Alcohol-induced pancreatitis generally showed a higher CTSI and more severe clinical course than pancreatitis caused by biliary tract disease. CONCLUSION: In the evaluation of acute pancreatitis, CTSI can be a useful predictor of its prognosis.