Pancreatoblastoma is a rare pancreatic tumor with a distinctive histologic appearance that generally affects infants and young children. We have studied 14 cases of pancreatoblastoma and reviewed 41 previously reported examples. Nine of our cases occurred in children (from newborn to 4 years old: mean, 2.4), and five affected adults (from 19 to 56 years old; mean, 40). There were 8 male cases and 6 female cases. Most patients presented with incidental abdominal masses, although pain, weight loss, and obstructive jaundice were present, but rarely. The tumors were very cellular microscopically, with cytologically uniform epithelial cells arranged in sheets and nests. Well-formed acinar structures were a consistent feature, and several cases contained ectatic ductular formations, rarely exhibiting intracellular mucin. Consistently present were squamoid corpuscles: circumscribed, whorled nests of plump spindle cells with a squamous appearance and occasional keratinization. The stroma was moderate to abundant and frequently quite cellular (especially in the pediatric cases). By immunohistochemistry, the tumors exhibited acinar, endocrine, and ductal differentiation, with positivity for pancreatic enzymes (100%), endocrine markers (82%). Ultrastructural examination most commonly revealed acinar differentiation, although mucigen granules and neurosecretory granules were also occasionally found. The behavior was variable: 36% of patients developed metastases, especially to the liver. The adult patients did poorly: three of five died of tumor (mean survival, 18 months), and two were alive at 5 and 15 months, respectively. In contrast, five of the six evaluable pediatric patients were alive from 22 months to 22 years after diagnosis, and only one died of tumor after 16 months. Good responses to chemotherapy were noted in the pediatric group.