The problems encountered in draining the bile ducts endoscopically in 148 patients with malignant obstruction of the mid or distal common bile duct and/or the papilla were assessed. Endoscopically visible extrinsic invasion of the papilla by a malignancy in the pancreatic head, with or without duodenal stenosis, appeared to be the major reason for the failure to insert a stent. The larger a tumor in the pancreatic head the greater the chance of invasion of the papillary region. This appeared to be evident for tumors restricted to the non-uncinate region of the pancreatic head. We would recommend primary percutaneous biliary drainage or surgery when the size of a proven malignancy restricted to the non-uncinate region of the pancreatic head is 5 cm or more, or when diagnostic duodenoscopy reveals extrinsic invasion of the papilla of Vater, or severe duodenal involvement with stenosis.