Ductal adenocarcinoma is the most common tumor type of cancer of the pancreas. It is generally a poorly demarcated, white to grey-solid tumor located in the pancreatic head. Histologically, it is often well-to moderately-differentiated tubular adenocarcinoma along with marked desmoplastic change. There are three well-defined precursors to invasive cancer; mucinous cystic neoplasms (MCNs), intraductal papillary mucinous neoplasms (IPMNs), and pancreatic intraepithelial neoplasia PanINs. PanIN is now considered to be a precursor of pancreatic ductal adenocarcinoma based on molecular studies. However, it is difficult to distinguish between small IPMNs and PanINs pathologically because both of them often show similar epithelium with cytoplasmic mucin. IPMNs and MCNs can form similar invasive carcinomas such as tubular adenocarcinoma and/or mucinous carcinoma. Another focus of this review is the issue of pathologic evaluation of the surgically resected specimens. Histologic grading and pathologic staging of each case are important especially in terms of the clinical aspects. Careful attention should be paid to the processes and/or criteria of pathologic diagnosis.