AMONG the heterogeneous group of developmental anomalies known as enteric duplications, mediastinal gastric cysts are of outstanding surgical importance, because without operative treatment they are almost invariably fatal. In the general category of mediastinal tumors, gastric cysts are extremely rare. Unlike other mediastinal cysts they are almost never asymptomatic. For this reason they are discovered in disproportionate numbers in the first decade of life and are actually one of the commonest mediastinal cysts encountered in infancy. Until recently, comparatively few examples of successful excision of these cysts have been reported, most of the cases being discovered at autopsy. Within the last five years the number of cases reported has almost doubled and practically all the recent articles record successful operations. We have been able to find 32 examples of intrathoracic gastric cysts1 in the literature. In the report that follows an additional case will be described. This infant was