Acinar cell carcinomas (ACCs) of the pancreas are characterized by the histological and immunohistochemical features of acinar cell differentiation. Recently, BCL10, originally identified as a recurrent t(1;14)(p22;q32) translocation in MALT B-cell lymphoma, was found to be immunohistochemically positive in some solid tumors, including ACC. To evaluate its diagnostic efficacy, we performed BCL10 immunohistochemistry and evaluated molecular markers correlated to pancreatic tumor lineages (neuroendocrine markers and a mutation analysis of KRAS and GNAS) using samples from 126 pancreatic tumors (17 ACCs, 24 pancreatic ductal adenocarcinomas, 4 adenosquamous carcinomas, 9 intraductal papillary mucinous neoplasms, 10 mucinous cystic neoplasms, 44 neuroendocrine tumors, 9 serous cystic tumors and 10 solid-pseudopapillary neoplasms). BCL10 was exclusively expressed in normal acini. In pancreatic tumors, 14 of 17 (82%) ACCs and 2 of 4 (50%) adenosquamous carcinomas were positive, while the other subtypes were almost negative. We subsequently examined the diagnostic utility of BCL10 in endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) specimens using 57 pancreatic tumors. BLC10 correctly identified ACCs (9/13) and adenosquamous carcinomas (2/4) but none of the other subtypes (n = 41). Therefore, we suggested that BCL10 expression is a useful marker for acinar cell differentiation, particularly in the diagnosis of EUS-FNA specimens.