A young patient presented with a rare tumour of the mediastinum. The first sign was liquid effusion in the right hemithorax. A major rise in alpha-foeto-protein level to 34,000 ng/ml rapidly led to diagnosis. Histological confirmation was obtained on a surgical biopsy specimen of the lung. Management included primary polychemotherapy followed by complete surgical exeresis. A second post-operative cycle of chemotherapy was given but only led to temporary normalization of alpha-foeto-protein levels and intensive chemotherapy followed by autograft to peripheral stem cells was performed. The vitellin tumour is a primary germ cell tumour usually observed in young men. It originates in extraembryonary primary mesenchymal tissue. Like other germ cell tumours, the diagnosis should be entertained for all tumours of the anterior mediastinum. Tumour markers useful for diagnosis and prognosis are beta-HCG, AFP and CEA. Levels above 500 ng/ml confirm vitellin tumour. Chemotherapy should be instituted rapidly using a BEP protocol (bleomycine, etoposide, cisplatinium) or a PVB protocol (cisplatinium, vinblastin, bleomycine). Using these new drugs and current therapeutic protocols, the rate of complete remission has risen from 13% to 40%.