Ectopic secretion of beta-subunit of human chorionic gonadotropin (β-HCG) in pulmonary pleomorphic carcinoma is remarkably rare. Such unusual ectopic hormone production by lung cancer may be initially misinterpreted as extragonadal choriocarcinoma or germ cell tumor. We report a 56-year-old postmenopausal female, smoker, who presented a 5-month history of progressive dyspnea, dry paroxysmal cough, and significant weight loss. She was referred by a local hospital with the preliminary diagnosis of gestational trophoblastic neoplasia due to a rapidly growing thoracic tumor with persistently elevated serum β-HCG. Computed tomography of the chest showed a lung mass in the right upper lobe associated with homolateral pleural effusion. Positron emission tomography showed pathological 2-[18F]FDG uptake at the mass lesion. Biopsies were performed. Histological examination described pleomorphic carcinoma with positive immunostaining for β-HCG. The serum levels of β-HCG were also elevated indicating ectopic secretion. The patient had rapid clinical deterioration and deceased before chemotherapy initiation. Only a few cases of paraneoplastic β-HCG secretion have been reported in the literature. Previous studies suggested that the ability to secrete β-hCG in tumors may correlate to some extent to chemoresistance; thus, it might be useful as a prognosis marker.