The aim of this study was to review the pathology of acute pancreatitis, resolving acute pancreatitis and chronic pancreatitis in order to find an answer to the unresolved question as to whether chronic pancreatitis is a primary disease or may be due to recurrent acute pancreatitis. Our series consisted of 71 pancreatic resection specimens and 15 autopsy pancreases from 8 patients with acute pancreatitis, 5 patients with pancreatitis 5-7 weeks prior to examination (resolving acute pancreatitis), and 66 patients with chronic pancreatitis. Peripancreatic and intrapancreatic fat necrosis was the key finding in acute pancreatitis. Organization of fat necrosis with early perilobular fibrosis and/or peripancreatic pseudocysts characterized the pancreas with resolving acute pancreatitis. Pseudocysts were present in 52% of pancreases with an early stage of chronic pancreatitis that was characterized by a focally accentuated fibrosis of the perilobular and, to a lesser degree, intralobular type. Marked fibrosis, ductal distortions and presence of intraductal calculi were the main features of advanced chronic pancreatitis. Pseudocysts were less frequent (36%) than in the early stage of the disease. On the basis of these findings it is suggested that acute pancreatitis, if it is severe and also affects the intrapancreatic fat deposits, may evolve into chronic pancreatitis.