The author report a case of isolated choriocarcinoma of the lung revealed in a young woman by a tumoral syndrome of the right base with haematoma. The diagnosis of isolated pulmonary choriocarcinoma was based on the lack of previous gynaecological history and tumour, on the singleness of the lung tumour at CT, and on the high initial beta-CGH level (3,300 ng/ml) in the absence of pregnancy. Surgical resection confirmed the diagnosis and lowered the beta-CGH level to 7 ng/ml. The various aetiopathogenic theories put forward and their relations with the prognosis disparity found in the literature are reviewed. The authors compare the prognosis of isolated pulmonary choriocarcinoma in a non-nulliparous woman to that of placental choriocarcinoma.