Lung cancer accounts for the highest malignancy-related mortality and more recent advances in targeted and immunotherapy have demonstrated the pivotal role of a thorough diagnostic work-up for appropriate therapeutic decision-making and long-term clinical outcome. This especially applies to pulmonary adenocarcinoma which can be subclassified depending on the histological growth pattern, immunohistochemical staining and the molecular profile. Fetal Adenocarcinoma of the Lung (FLAC) is a rare subtype of pulmonary adenocarcinoma which comprises two pathologically distinguishable variants. In this case report we present a 65-year-old male who referred to our clinic with exertional shortness of breath, increased sputum, and one-sided upper arm paresis. The pathological examination of a well-demarcated oval mass with a cranio-caudal extension of 12 cm in the right upper lobe led to the diagnosis of High-grade Fetal Adenocarcinoma of the Lung (HFLAC).