Swyer-James (MacLeod) syndrome is an acquired form of unilateral hyperlucency of the lung and is characterized by the development of severe emphysema, bronchiectasis, and/or bronchiolitis obliterans. It may develop as a complication of repeated episodes of pulmonary infection resulting in bronchiolitis obliterans and obstruction of small airways. Most patients with Swyer-James (MacLeod) syndrome can be managed clinically, and the pathologic features of the syndrome have been described in only a few reports. Placental transmogrification of the lung is a rare histopathologic finding that has been described in patients with severe emphysema associated with cigarette smoking, congenital bullous emphysema, and fibrochondromatous hamartomas of the lung and is characterized by the development of peculiar structures in the pulmonary parenchyma that resemble placental villi. To our knowledge, placental transmogrification of the lung has not been previously described in patients with Swyer-James (MacLeod) syndrome. We encountered a 32-year-old man with a history of childhood asthma who presented with progressively severe exertional dyspnea and had unilateral right lung hyperlucency. The patient underwent a right pneumonectomy. Examination of the lung revealed severe mixed centriacinar-panacinar emphysema in all lobes, bullous emphysema in the upper lobe, bronchiectases, mild interstitial pneumonia with fibrosis, and placental transmogrification of the pulmonary parenchyma of all 3 lobes. Here, we review the pathology of Swyer-James (MacLeod) syndrome and the possible pathogenesis of villous-like changes in the lung tissues.