BACKGROUND AND AIMS: Traditionally, the severity of acute pancreatitis has been predicted by Ranson's prognostic sign and computed tomography (CT) grade. The aim of this study was to verify the correlation between Ranson's prognostic sign and CT grade in the evaluation of the severity of acute pancreatitis. METHODS: For 66 patients with acute pancreatitis, clinical course, Ranson's prognostic signs and CT grade were analysed retrospectively. The clinical course was assessed by admission day, mortality and deveIoped complications. The correlation between Ranson's prognostic signs and CT grade was analysed. RESULTS: Admission day was increased according to increase in CT grade (A, 10.4; B, 17.8; C, 16.2; D, 20.1; E, 23.4 days) and Ranson's prognostic signs (0, 11.7; 1, 13.6; 2, 16.8; 3, 24.2; more than 4, 26.7 days). A patient with CT grade and Ranson's prognostic sign 6 died of respiratory failure and renal failure. The correlation between Ranson's prognostic sign and CT grade was not significant. CONCLUSIONS: The Ranson's prognostic sign and CT grade are good predictors of acute pancreatitis. However, the significant correlation between Ransan's prognostic sign and CT grade is not detected. The prognosis of acute pancreatitis may be evaluated by both Ranson's prognostic sign and CT grade.