Four tumors with histologic, histochemical, and ultrastructural characteristics of papillary cystic neoplasm of the pancreas but lacking the capsule commonly observed in papillary cystic neoplasm and infiltrating interiorly into the pancreatic parenchyma were seen in two men and two women who were 39 to 51 years old. These tumors contrasted with typical encapsulated papillary cystic neoplasms that show extrapancreatic growth and that are detected as a palpable abdominal mass in young women. These four tumors, although unpalpable, were all detected by nodular images of calcification in abdominal plain radiography. The tumors had a mean diameter of 3.1 cm (range, 1.7 to 4.5 cm), were confined within the pancreatic parenchyma, and showed central fibrosis accompanied by dystrophic changes such as calcification and ossification. A small necrotic cyst contiguous to the fibrous focus also was observed in the tumor in three patients. Tumor cells similar to those of a papillary cystic neoplasm had infiltrated among the pancreatic parenchyma in solid and pseudopapillary patterns, and pleomorphic atypism was observed in some parts of the tumor in three patients. These tumors were tentatively designated solid, infiltrating variety of papillary cystic neoplasms to differentiate them from ordinary encapsulated papillary cystic neoplasms. Although no signs of recurrence have been noticed after surgical treatment in these patients, the infiltrating growth pattern and the presence of pleomorphic atypism suggest higher malignancy than the ordinary papillary cystic neoplasm. The contrasting growth pattern and possible malignancy may warrant establishment of these tumors as a papillary cystic neoplasm subclass.