Pancreatic pseudocysts in 83 patients were classified according to clinical and radiographic criteria. Group I (45 patients) had acute, 'post-necrotic' pseudocysts with normal pancreatic duct anatomy and rarely duct-pseudocyst communication. Percutaneous drainage was curative in all patients in whom it was used. Group II (26 patients) included 'post-necrotic' pseudocysts developing in patients already suffering from chronic pancreatitis. The pancreatic duct was diseased but not strictured, and duct-pseudocyst communication was often present. Percutaneous drainage is possible for such patients but it may have to be prolonged; surgical internal drainage was usually successful. Group III (12 patients) had chronic 'retention' pseudocysts. The pancreatic duct was grossly diseased and strictured and duct-pseudocyst communication was present in all cases. Percutaneous drainage is contraindicated and surgical internal drainage has a high recurrence rate. Operative procedures in this group should address the specific ductal pathology. An improved classification of pseudocysts could help the surgeon to choose the most appropriate form of treatment.