When PPB was first described, it was necessary to distinguish it carefully from the adult-type pulmonary blastoma. The uniqueness of childhood PPB now is widely accepted. PPB tends to occur in young children. Adult pulmonary blastoma is a biphasic neoplasm with malignant glandular (epithelial) and mesenchymal components. In contrast, childhood PPB is exclusively sarcomatous, without a carcinosarcomatous component. Adult pulmonary blastoma is often focal, has a bimodal age distribution in young and middle-aged adults, and presents in adults with a history of smoking.