Background: Pulmonary placental transmogri. cation (PT) is a rare and benign lesion that was first described in 1979. Pathology of the disease is characterized by the formation of papillary structures similar to placental villi surrounding the pulmonary epithelium. Case Report: We report a case of pulmonary placental transmogrification in a 66-year-old woman who presented with a single nodule. She had been controlled well for her diabetes mellitus and hypertension. She did not complain of any respiratory or systemic symptoms. Chest radiography showed focal ill-de. ned nodular opacity at right lower lobe. Chest computed tomography (CT) scan revealed about 17mm lobulated and focal irregular mass with fissural retraction in right lower lobe that suggested lung cancer. The pathology from percutaneous needle aspiration biopsy observed papillary structures, resembling placental villi, within the hyperin fiated cystic spaces. It was negative for thyroid transcription factor-1 (TTF-1) and partly positive for Ki-67 in immuno-histochemical staining. Discussion: Clinically, this disease is known commonly occurring between 20 to 50 year-old male and usually presented with dyspnea or pneumothorax. However, in this case, it is occurred in a female patient with no symptom. PT may not be a variant of giant bullous emphysema, but interstitial clear cell proliferation with secondary emphysema-like cystic change. In our case, interstitial clear cell proliferation findings were only observed without emphysema-like cyst. Based on previous cases, the patients who were left untreated upon diagnosis of PT have, in many cases, proceed in suffering severe complications such as bullous emphysema, recurrent pneumothorax or tension pneumothorax. Thus, early diagnosis as well as closed follow up is considered critical as in our case. Unfortunately, The final diagnosis of PT is only possible from histologic and immunologic findings. Further studies may provide to clarify pathogenesis of PT.