We report a case of well-differentiated fetal adenocarcinoma (WDFA) of the lung, with emphasis on dynamic CT (computed tomography) findings. The patient was a 38-year-old woman who was found to have a mass in the left upper lung field in chest radiograph screening. Chest radiograph showed a 5.5 cm well-defined mass in the left upper lung field. CT revealed a well-circumscribed mass measuring 5.5 × 5.5 × 5.0 cm with a lobulated margin in the left upper lobe. Intratumoral enhancing vasculature was noted in the early phase of dynamic CT. In the delayed phase, persistent and plateau enhancement was seen. The tumor also had consistently unenhanced areas, suggesting the presence of necrosis. Left upper lobectomy with mediastinal lymph node dissection was performed. The pathology specimen contained tubular glands consisting of non-ciliated columnar cells with areas of solid nests of epithelial cells with weakly eosinophilic cytoplasm (morule) mimicking fetal lung tissue. The tumor was moderately vascularized with areas of comedo necrosis; the stroma was relatively scanty. Final pathological diagnosis was WDFA with left hilar lymph node metastasis (stage T2bN1M0). This is the first report of dynamic CT findings of WDFA, a rare lung tumor. Although these findings are non-specific, they well reflected the pathological characteristics of this tumor.