We describe a purely intraductal acinar cell carcinoma involving branch ducts of the pancreas in a 74-year-old man, which presented as recurrent episodes of acute pancreatitis. Endoscopic ultrasound examination revealed an intraductal mass bulging into the main pancreatic duct suggesting, pre-operatively, an intraductal mucinous papillary tumour. Gross examination showed several dilated branch ducts that contained haemorrhagic tumour material without any solid or true cystic formation within the pancreatic parenchyma. Using histology, a purely intraductal acinar cell carcinoma was observed, involving branch ducts only, associated with foci of carcinoma in situ in adjacent exocrine parenchyma. The main pancreatic duct was free of disease except for its communication with a cancerous branch duct. A concomitant neuroendocrine microadenoma was incidentally found during slide screening. Immunohistochemistry performed on the intraductal proliferation confirmed zymogen secretion with positive staining for alpha-1 anti-chymotrypsin and anti-trypsin and the persistence of diastase-periodic acid-Schiff positive granules in the apical pole of the tumour cells. Neuroendocrine markers were negative in the acinar cell carcinoma and positive in the neuroendocrine microadenoma. To our knowledge, this is the first report of an intraductal acinar cell carcinoma of the pancreas involving branch ducts and sparing the main pancreatic duct.