Our objective was to determine whether pleural effusion is a predictor of severity in acute pancreatitis and, if so, whether it is an independent predictor. One hundred ninety-six consecutive cases of acute pancreatitis from October 1, 1994, to September 30, 1995, were reviewed. Medical records were analyzed for evidence of pleural effusion by chest radiograph and severe acute pancreatitis by identification of pancreatic necrosis or organ system dysfunction. Data were analyzed to determine if identification of pleural effusion provided an early sign of severity. Among 135 patients who underwent chest radiography, pleural effusion was seen in 16 of 19 (84.2%) with severe pancreatitis and 10 of 116 (8.6%) of patients with mild pancreatitis (p< 0.001). Pleural effusion was noted in severe pancreatitis prior to clinical or computed tomography evidence of severity in only 20% of cases. Pleural effusion is strongly associated with severity in acute pancreatitis but provides independent information on severity in only a minority of cases.