Pancreatic pseudocysts are a common finding in acute-and chronic pancreatitis, but most are small and uncomplicated, and do not require treatment. Pseudocysts with splenic parenchymal involvement are uncommon but have the potential for massive hemorrhage. Data on the clinical presentation and optimal treatment of this unusual complication of pseudocysts are lacking. The purpose of this review was to identify the clinical features of pancreatic pseudocysts complicated by splenic parenchymal involvement and to determine the outcome with nonoperative and operative therapy. Methods: A retrospective review of the medical records of all patients with pancreatic pseudocysts from December 1984 to January 1999 revealed 238 patients, of whom 14 (6%) had splenic parenchymal involvement. These medical records were reviewed in detail and all pertinent radiographs were reviewed by the authors to confirm splenic parenchymal involvement by a pancreatic pseudocyst. Results: initial treatment included observation (n = 2) percutaneous drainage (n = 8), and surgery (n = 4), Of the eight patients treated by percutaneous drainage. one died, three required repeated percutaneous drainage. and three required surgical intervention, None of thr patient, treated primarily by surgery required additional therapy for the pseudocyst. Overall, 11 patients had complications of the primary therapy. and 25% of patients treated by surgery had significant hemorrhage. Complications included infection (n = 5), pseudocyst persistence (n = 4), bleeding (n = 2), multisystem organ failure (n equivalent to 2), gastric outlet obstruction (n = 1), and splenic rupture (n = 2). Conclusions: Pancreatic pseudocysts complicated by splenic parenchymal involvement may have life-threatening clinical presentations and respond pool ly to percutaneous drainage. Distal pancreatectomy and splenectomy are effective, but thr complication rate is high.