Five patients with peripancreatic abscesses associated with severe acute pancreatitis were treated by hyperbaric oxygen therapy (HBO). In 3 patients, the course after surgical mobilization of the pancreas and drainage of the pancreas bed was complicated by peripancreatic abscesses. HBO was conducted under a pressure of 2.8 atmospheres for two hours daily. Four of the 5 patients showed a progressive improvement in their condition. In one patient who failed to respond despite seven sessions of HBO, Pseudomonas aeruginosa was isolated from the discharge, and resection of necrotic tissue and drainage were performed. The main effects of HBO were the alleviation of high spiking fever, the improvement of white blood cell count and serum amylase levels, and the reduction of the abscess size. We recognized HBO to be a successful treatment for peripancreatic abscess associated with severe acute pancreatitis and better results were obtained than in cases that did not receive HBO.