The authors report the case of a patient in whom an antenatal ultrasound showed a mediastinal tumor then a pleural effusion. At birth, the baby was intubated for adequate ventilation and pleural effusion was drained. Ultrasound, oesophagogram, CT scan permitted the diagnosis of tubular oesophageal duplication which was confirmed by surgery and pathologic examination. Review of the literature did not find such antenatal finding. The role of oral contraception during the first weeks of pregnancy is discussed.