Pancreatic intraepithelial neoplasia (PanIN) may be difficult to differentiate from isolated glands of pancreatic adenocarcinoma. We studied the normal relationship between the pancreatic ducts and the pancreatic muscular blood vessels in 126 pancreata, 64 of which were removed for pancreatic adenocarcinoma and 62 for other diagnoses. We also examined the effects that atrophy and PanIN have on this relationship. In normal pancreatic parenchyma and in mild to moderate atrophy, blood vessels are guideposts of the interlobular space. The pancreatic acinar parenchyma ensheathes the pancreatic ductal system and separates it from the muscular pancreatic vasculature. Since these blood vessels do not accompany the pancreatic ducts, the presence of a well-differentiated duct-like structure, which may resemble PanIN, located adjacent to a pancreatic blood vessel should be a clue to the infiltrative and hence malignant nature of that gland. Ducts showing PanIN appear to resist atrophy. Since lobular outlines and vascular landmarks are ultimately lost in severe atrophy, they cannot be relied on to aid in the distinction between PanIN and invasive carcinoma. However, it is unusual to see PanIN1 in such severe atrophy (2%), and although the normal vascular landmarks are no longer there to aid in the interpretation, the presence of well-differentiated duct-like structures resembling PanIN1 in this background should be viewed with suspicion for well-differentiated adenocarcinoma.