A case of histologically and ultrastructurally confirmed acinar-cell carcinoma of the pancreas examined by needle aspiration cytology is reported. The aspirate showed isolated and loosely clustered cells with variable granular cytoplasm, and central or eccentrically located oval hyperchromatic nuclei displaying prominent nucleoli, suggesting a pancreatic neuroendocrine tumor. Numerous intracytoplasmic zymogen granules and several microtubules within cisternae of rough endoplasmic reticulum (MCRER) were found by electron microscopic study of metastatic tumor tissue. Cytodiagnostic pitfalls of this rare pancreatic cancer are discussed as well as the diagnostic value of MCRERs.