Among 27 surgically resected carcinomas of the pancreas, 3 cases were diagnosed histologically as adenosquamous carcinoma (11.1%). This is the highest rate among the medical literature we reviewed. Since a very small focus of squamous cell carcinoma was detected through close observation in 1 case, it would seem that this sort of pancreatic tumor could be more common than is ordinarily expected. From the histologic studies of these 3 cases, it seems likely that the preexisting adenocarcinoma partially underwent malignant transformation into a malignant squamous component. When the different modes of spread of these two histologic elements are compared, the adenocarcinomatous element seems to be more invasive and more likely to metastasize than does squamous cell carcinoma.