Acute pancreatitis is characterized by the occurrence of necroinflammatory changes in the pancreas. Three types of necrosis may be distinguished: (1) interstitial tissue necrosis, which subsequently may also involve acinar and ductal cells, (2) ductal necrosis, and (3) acinar necrosis. The first type of necrosis is autodigestive in nature and is typical of the most common forms of acute pancreatitis, which are associated with alcohol, bile duct disease, metabolic conditions, and other rare factors. Clinically, these types of pancreatitis may be either mild or severe (Atlanta classification). The mild form is also known as edematous pancreatitis, because there is edematous swelling of the pancreas combined with tiny foci of interstitial (fat) necrosis. Severe or necrotizing pancreatitis shows large areas of often hemorrhagic necrosis of the pancreatic and particularly the peripancreatic tissue. The ductal type of necrosis is rare and may be seen in pancreatitis associated with prolonged circulatory failure. The acinar type of necrosis is caused by infectious agents. Complications of acute pancreatitis, such as pseudocyst, bleeding, and infection, determine the course of the disease.