Fourteen cases of solid-cystic tumor of the pancreas have been investigated at the ultrastructural level. A heterogeneous cell population has been found, and some distinctive features have been identified: oncocytoid cells; clear cells reminiscent of ductular and centro-acinar cells; cells with exocrine and endocrine features; cells with bundles of microfilaments and dense bodies, reminiscent of myoepithelium. This varied differentiation strongly suggests the tumor histogenesis to be from multipotent cell capable of recapitulating the normal ontogenesis during its neoplastic proliferation. Furthermore, the heterogeneity in ultrastructural appearance is a characteristic and reliable feature of solid-cystic tumor of the pancreas.