Acute mediastinitis is a fatal disease that usually originates from esophageal perforation and surgical infection. Rare cases of descending necrotizing mediastinitis can occur following oral cavity and pharynx infection or can be a complication of pancreatitis. The most common thoracic complications of pancreatic disease are reactive pleural effusion and pneumonia, while rare complications include thoracic conditions, such as pancreaticopleural fistula with massive pleural effusion or hemothorax and extension of pseudocyst into the mediastinum. There have been no reports of acute mediastinitis originating from pancreatitis in South Korea. In this report, we present the case of a 50-year-old female suffering from acute mediastinitis with pleural effusion arising from recurrent pancreatitis that improved after surgical intervention.