In this article we describe the current status of treatment of acute pancreatitis in Japan and the guidelines established for the treatment of severe acute pancreatitis. In 1987 the Research Committee for Intractable Diseases of the Pancreas of the Ministry of Health and Welfare conducted a nationwide survey on acute pancreatitis to determine the prevalence of the disease between 1982 and 1986 and the treatment modalities used. Based on a detailed assessment of the results of the survey, the Committee developed criteria for rating the severity of acute pancreatitis and guidelines for the treatment of acute pancreatitis, which was revised in 1995. The five points cited as the principal aspects of treatment of severe acute pancreatitis in Japan include (a) rating the severity of the disease according to the severity rating criteria; (b) differentiating between edematous and necrotic pancreatic lesions and performing dynamic CT of the pancreas to define the extent of pancreatic necrosis; (c) performing ultrasonography to determine whether there are gallstones; (d) in principle, not performing surgery except in patients who clearly have early infection or complications after the onset; and (e) providing conservative intensive care immediately after the onset. In the absence of complications, the treatment of acute pancreatitis in Japan is primarily medical. In contrast to other countries, however, administration of antiprotease agents has become an important method of treating acute pancreatitis in Japan. Special treatment modalities, such as peritoneal lavage, blood purification, and continuous arterial infusion of protease inhibitor, are being performed in severe acute pancreatitis, in addition to intensive care.