A thorough histologic examination of the pancreas was performed on autopsy material from 83 military veterans aged 35-88 years. Hyperplastic, preneoplastic and neoplastic alterations were recorded by severity, multiplicity, location and age. From this material, two patients had clinically known primary, and three had secondary (metastatic), pancreatic cancer. The following occult malignant lesions were found: two early cancers (one adenocarcinoma and one adenosquamous cell carcinoma), one ductal carcinoma in situ and seven ductular carcinomas in situ. Among patients with ductular carcinoma in situ, three had pancreatic caner and the remaining four had cancers of other sites (ethmoid, ear, colon, prostate). One patient who was clinically diagnosed as having lung cancer with selective metastases to the pancreas was found to have pancreatic adenosquamous cell carcinoma with lung metastases. Hence, the incidence of neoplastic exocrine lesions was around 10%. In addition, hyperplasia of the ductal and ductular epithelium (in 57% and 39% of the patients, respectively), squamous cell metaplasia of the ductules (in 48% of the cases), as well as endocrine tumors (islet cell adenoma, 10%; mixed ductular-insular adenoma, 3%) were found. Most lesions occurred in the pancreatic head, a few in the tail. These data and other reports led to the conclusion that, first, the overall incidence of pancreatic cancer appears to be higher than previously reported. Malignant lesions seem to remain clinically occult, either because patients die of other diseases or because of the significantly long latency between premalignant lesions and clinically recognizable invasive cancer. Second, the ductular cells appear to be the progenitor cells of a variety of tumor types, including squamous cell cancer and islet cell tumors, as in the authors' experimental model.