Objective To explore the relationship between computed tomography severity index(CTSI) and prognosis of severe pancreatitis. Methods We performed a retrospective review of 185 patients admitted to our hospital from 1994 to 2000 with a diagnosis of acute pancreatitis. The CTSI of acute pancreatitis was calculated by Balthazar criterion, at the same time the death rate, time of hospitalization, and need for necrosectomy were measured. Their relationships were compared one another. Results CTSI significantly correlated with death, prolonged hospital stay and need for necrosectomy ( P 0.05-0.005). Patients with CTSI 5 were 9 times more likely to die, 35 times more likely to have a prolonged hospital course, and 15 times more likely to undergo necrosectomy than their counterparts with CTSI5. Conclusion CTSI plays an important role in evaluating the severity degree and prognosis of acute pancreatitis.