Two cases of placental transmogrification of the lung are reported. The lesions presented in the left lung, in one case as a giant bulla of the upper lobe and in the other as a cystic nodule of the lower lobe. A segmentectomy was performed in both cases, and the patients were alive and well 5 years and 2 months after surgery, respectively. In our opinion, pulmonary placental transmogrification is not a variant of emphysema, as generally considered, but rather probably represents a benign proliferation of immature interstitial clear cells with secondary cystic change. This report presents a histological, immunohistochemical, ultrastructural and molecular study of these peculiar cells, together with a review of the literature.