To evaluate whether obesity is a negative prognostic parameter in the course of acute pancreatitis, we examined 149 patients and divided them into four weight groups. Single (methemalbumin) and multiple (Ranson's signs) prognostic parameters were found to be independent of increased body weight in all groups, although the incidence of patients with more than six Ranson's signs or a positive methemalbumin test was highest in the most obese group. There was also no direct positive correlation between increased body weight and the incidence of mortality and late complications such as pseudocysts and abscesses. However, when compared with patients of normal weight, the obese groups showed a slight increase in the incidence of early complications such as shock and renal insufficiency and a significant increase in respiratory insufficiency necessitating artificial ventilation. Thus, increased body weight was associated with increased incidence of early extrapancreatic complications.