We report a case of well-differentiated fetal adenocarcinoma (WDFA), which is a variant of pulmonary blastoma. A 36-year-old man was found to have a tumor shadow in the right middle field of a chest radiograph as part of a mass screening examination, and chest computed tomography (CT) showed a 4.5-cm pulmonary mass in the right lower lobe. A diagnosis of adenocarcinoma of the lung was made based on a CT-guided needle biopsy, and right middle and lower lobectomy and lymph node dissection were performed. The postoperative pathological diagnosis was well-differentiated fetal adenocarcinoma. WDFA has a better prognosis than conventional pulmonary blastoma (biphasic pulmonary blastoma). We summarize the cases of WDFA reported in Japan and review the literature.