Nine female patients with papillary-cystic neoplasms (PCN) of the pancreas were studied clinicopathologically. The ages of seven of these patients ranged from 8 to 24 years. The remaining two patients, who were 47 and 60 years of age, were considered to have had the onset in their youth. There were few subjective symptoms, and the lesion was most often detected as a palpation of a mass by the patients themselves. Although the prognosis was generally favorable, the two older patients died of metastases. This suggested low-grade malignancy of PCN. The tumors were large (6.9 cm in mean diameter) and encapsulated, and their cross-sections showed an intermingling of solid tumoral areas and cystic necrotic areas. The histologic features of the solid tumoral portion were relatively uniform, with the tumor cells showing solid and pseudopapillary or pseudoglandular proliferation but few mitoses or atypism. Histochemical, immunohistochemical, and electron microscopic examinations showed polymorphic differentiation, which means that part of the tumor cells differentiated into duct epithelium, acinus, and endocrine cells (primary constituents of the pancreas). These findings suggest that the origin of PCN is totipotential primordial cells found in the development of the embryonic pancreas.