We report a case of a large posterior mediastinal neurenteric cyst in a neonate demonstrated by chest radiographs, barium swallow examination, ultrasonography and CT of the thorax. All the investigations revealed a large posterior mediastinal cystic mass with vertebral anomalies in the form of scoliosis and hemivertebra. The cyst was completely excised by a right posterolateral thoracotomy and biopsy showed the features of a neurenteric cyst. The rarity of the lesion prompted us to report this case.