MicroRNAs have potential as diagnostic cancer biomarkers. The aim of this study was (1) to define microRNA expression patterns in formalin-fixed parafin-embedded tissue from pancreatic ductal adenocarcinoma, ampullary adenocarcinoma, normal pancreas and chronic pancreatitis without using micro-dissection and (2) to discover new diagnostic microRNAs and combinations of microRNAs in cancer tissue. The expression of 664 microRNAs in tissue from 170 pancreatic adenocarcinomas and 107 ampullary adenocarcinomas were analyzed using a commercial microRNA assay. Results were compared with chronic pancreatitis, normal pancreas and duodenal adenocarcinoma. In all, 43 microRNAs had higher and 41 microRNAs reduced expression in pancreatic cancer compared with normal pancreas. In all, 32 microRNAs were differently expressed in pancreatic adenocarcinoma compared with chronic pancreatitis (17 higher; 15 reduced). Several of these microRNAs have not before been related to diagnosis of pancreatic cancer (eg, miR-492, miR-614, miR-622). MiR-614, miR-492, miR-622, miR-135b and miR-196 were most differently expressed. MicroRNA profiles of pancreatic and ampullary adenocarcinomas were correlated (0.990). MicroRNA expression profiles for pancreatic cancer described in the literature were consistent with our findings, and the microRNA profile for pancreatic adenocarcinoma (miR-196b-miR-217) was validated. We identified a more significant expression profile, the difference between miR-411 and miR-198 (P=2.06 × 10(-54)) and a diagnostic LASSO classifier using 19 microRNAs (sensitivity 98.5%; positive predictive value 97.8%; accuracy 97.0%). We also identified microRNA profiles to subclassify ampullary adenocarcinomas into pancreatobiliary or intestinal type. In conclusion, we found that combinations of two microRNAs could roughly separate neoplastic from non-neoplastic samples. A diagnostic 19 microRNA classifier was constructed which without micro-dissection could discriminate pancreatic and ampullary adenocarcinomas from chronic pancreatitis and normal pancreas with high sensitivity and accuracy. Ongoing prospective studies will evaluate if these microRNA profiles are useful on fine-needle biopsies for early diagnosis of pancreatic cancer.