Computed tomography is the single most important imaging modality in evaluating patients with acute pancreatitis. It has a high sensitivity and specificity in diagnosing "moderate" and "severe" pancreatitis, as well as in detecting serious complications which often are clinically unsuspected. In addition, computed tomography plays a valuable role as an early predictive indicator of disease severity. Patients with extrapancreatic phlegmonous collections and patients with pancreatic necrosis are considered to be at high risk to develop complications.