Pulmonary blastoma is a rare malignant tumor seen in both adults and children. Approximately only 25% of cases occur in pediatric patients, many of whom affected by a congenital pulmonary cystic lesion. The clinical features, radiological findings and management of a 3-year-old boy affected by a pulmonary blastoma which arose in a congenital cystic adenomatoid malformation are reported, and an extensive review of the literature is also made. Because of the well-known tendency of cystic pulmonary diseases to develop malignancies, authors recommend the surgical excision of these kind of lesion or at least their close radiological follow-up.