A 35-year-old man presented with high fever and abdominal pain. The patient was an alcoholic and acute pancreatitis had occurred repeatedly before this admission. Laboratory tests showed severe inflammation. CT imaging identified an enhanced cavity with a pseudocyst in the middle of the pancreatic body. The cavity contained fluid and air, and was thought to be an abscess penetrating to the stomach. EGD was performed, and detected a pocket filled with milky-white liquid in the posterior wall of the gastric upper body. Gastrography showed a fistula between the abscess and stomach. The fistula was expected to permit smooth drainage from the abscess. Intravenous antibiotics were administered for two weeks to control inflammation and diminish the abscess. Surgery was avoided in this patient and he was discharged 45 days later. Pancreatic pseudocyst is a common complication of pancreatitis. Small pseudocysts often resolve naturally. Large pseudocysts tend to cause infection, bleeding or rupture─requiring surgical treatment. In most cases reported in Japan, patients with pancreatitis and a large pseudocyst tend to be male alcoholics with hematemesis, requiring surgical treatment. Some publications report that percutaneous abscess drainage and somatostatin analogue use are effective in cases where bleeding is not present. Conservative treatment─using antibiotics and antacid─rarely cure the inflammation present with large pseudocysts.