Heterotopic pancreatic tissue is not uncommon. Although the cancerous transformation of heterotopic pancreatic tissue is a theoretical possibility, it is an extremely rare phenomenon. The majority of the heterotopic pancreatic malignancies reported in the literature are adenocarcinomas (32 cases). An Acinar Cell Carcinoma (ACC) arising from heterotopic pancreatic tissue is even less common with only six cases being reported. This report presents an extremely rare case of heterotopic pancreatic ACC presenting as a duodenal mass. We propose that heterotopic pancreatic ACC should be considered as a possibility in the differential diagnosis of a duodenal mass.