The role of obesity in acute pancreatitis has not been fully investigated. Based on the new internationally recognized classification system for acute pancreatitis since 1993, the aim of the present study is to evaluate the implications of obesity as an early prognostic indicator for the development of complications in the course of acute pancreatitis. Three hundred twenty patients with acute pancreatitis were consecutively evaluated in a prospective cohort study. Severe acute pancreatitis was defined by the development of organ failure and/or local complications. Obesity was evaluated by measurement of body mass index. The body mass index did not differ significantly between the patients who lived or died (P = 0.51). The obese (body mass index > or =30 kg/m2) had a higher incidence of developing local complications than the nonobese (P < 0.0001). There was no statistical difference in the incidence of developing systemic complications (P = 0.21) or in the mortality (P = 1.0) between the obese and nonobese. These data demonstrated that obese patients had a higher risk of developing local complications in the course of acute pancreatitis. Obesity did not carry an increased risk of developing organ failure or fatal outcome.