Objective To investigate the characteristics and prognosis of acute and chronic pancreatic pseudocysts and to identify the predictive factors of interventional treatment of pancreatic pseudocysts. Methods From January 1995 to December 2004, 36 patients with pancreatic pseudocysts at Nippon Medical School were studied retrospectively. Group 1 included 9 patients with acute pancreatitis associated pseudocysts which resolved spontaneously. Group 2 included 9 patients with acute pancreatitis associated pseudocysts and symptoms persisted or with complications which requiring interventional treatment. Group 3 included 9 patients with chronic pancreatitis associated pseudocysts which resolved spontaneously. Group 4 included 9 patients with chronic pancreatitis associated pseudocysts with symptoms persisted or with complications which requiring interventional treatment. Results Among the 36 patients, there were 13 women and 23 men. The etiology of pancreatitis due to alcohol was 18(50.0%) cases, biliary tract disease 8(22.2%)cases, others 10(27.8%) cases. The average duration of follow up was (24. 2 ± 18.5) months. The majority of pseudocysts (32/36, 88.9%) were not communicated with the main pancreatic duct;the number and location of the 4 groups of pseudocysts were not significantly different;the biggest diameter of pancreatic pseudocysts in group 3 was the smallest, all below 4 cm, which was significantly less than those in other 3 groups (P < 0.05) ;the majority of volume of pancreatic pseudocysts in group 1 and 3 was not increased, while it was increased in group 2 and 4.