A 30-year-old woman was admitted to our hospital for investigation of an abnormal shadow in the right pulmonary hilus on a chest X-ray film. A percutaneous needle biopsy was performed, which revealed pulmonary blastoma. A right upper lobectomy was performed and the pathological stage was confirmed to be IIIa (T3N0M0). An analysis of preoperative cytological specimens showed that epithelial tumor cells with thin cytoplasm were either tubular or papillary, while some mesenchymal tumor cells with elliptic and spindle-shaped nuclei were also found in the necrotic background. Thus, pulmonary blastoma should be considered when a two-cell pattern consisting of both epithelial and mesenchymal components is observed. DNA analysis was performed on previously identified areas of the epithelial or sarcomatous components, using a microdissection method. An analysis of the p53 gene by the single-strand conformation polymorphysm method showed an abnormal band with shifted mobility of exon 8 in only the sarcomatous component.