The literature is riddled with misconceptions concerning the landmarks and the actual amount of pancreatic tissue resected in "subtotal" 60% to 90% pancreatectomies. In order to clarify the surgical anatomy of the pancreas, 13 autopsy specimens from children aged 2 days to 15 years were carefully examined. Pancreata were serially removed from the in situ position in four sections and weighed. Section 1 included pancreatic tissue from the tail to the left of the superior mesenteric vessels (SMV); section 2 included all tissue from the tail to the right of the SMV; section 3 contained tissue up to the left of the pancreaticoduodenal vessels in the head of the pancreas; and section 4 included the remainder of the pancreatic head within the duodenal sweep and the uncinate process. Results showed that section 1 weighed 47.5% +/- 9.7% (mean +/- SD) of the total pancreatic weight with a wide range of 32.3% to 67.3%; section 2 weighed 53.5% +/- 9.0% (range, 38.7% to 72.2%); section 3 weighed 69.1% +/- 15.6% (range, 43.5% to 95.8%); and section 4 weighed 31.6% +/- 14.6% (range, 4.2% to 56.5%). As noted, pancreatic anatomy was extremely variable in relation to the percent of tissue to either side of the SMV and the proportion of tissue contained within the uncinate process. Resections historically reported to result in a "75%" pancreatectomy (section 2) were demonstrated to contain a mean of only 53.5% +/- 9.0% of the pancreas. Less tissue than expected would be resected by using the SMV as landmarks for a 75% resection. The wide variation in anatomy also has important clinical implications in performing "subtotal" pancreatectomies in infants with nesidioblastosis in whom the amount of tissue resected is critical to the patient's postoperative clinical course. This study demonstrates that a subtotal pancreatectomy should not be based upon the presumed relation of the pancreatic substance to the SMV. The entire gland including the uncinate process should be visualized at operation in order that a proper pancreatectomy is performed.