We reviewed the records of 32 adult patients with choledochal cysts (CDC) to determine the characteristics of the associated pancreatic disease. Eighteen patients (56%) had 30 documented episodes of pancreatitis with epigastric pain and elevated serum amylase levels. Three patients developed a prolonged course with a pancreatic phlegmon and one patient died secondary to a pancreatic abscess after endoscopic retrograde cholangiopancreatography (ERCP). Pancreatitis occurred in all types of CDC and was not related to the age, gender or race of the patient. There was an association with the size of the CDC: 90% of patients with CDC > or = 5 cm developed pancreatitis compared with only 9% of patients with CDC < 5 cm (p < 0.0004). In addition, ERCP was performed in 14 patients and demonstrated an abnormal pancreaticobiliary duct junction in eight (57%). All eight patients with an abnormal pancreaticobiliary junction developed pancreatitis compared with only 2 out of 6 patients with normal pancreatic duct anatomy (p < 0.006). Patients undergoing surgical bypass rather than resection also tended to have higher rates of pancreatitis (80 vs. 50%). One patient with a Type I CDC and chronic pancreatitis was treated with surgical resection of the CDC and pancreatic head; this combined procedure relieved the pain. Microscopic examination of the CDC and the abnormal "common channel" within the pancreas revealed identical fibrous thickening of the duct walls with focal chronic inflammation and loss of surface epithelium. In conclusion, these data stress the previously unrecognized high incidence of symptomatic pancreatic inflammatory disease that accompanies adult CDC.(ABSTRACT TRUNCATED AT 250 WORDS)