An incidental discovery of a posterior and inferior mediastinal cyst-like opacity allowed us to diagnose a pulmonary sequestration in a 45-year old woman. The operative findings showed an hour-glass tumor of the inferior mediastinum with an abdominal prolongation attached by a stalk onto the top of the stomach. These findings made us change our diagnosis in favour of an abdomino-thoracic gastric duplication. This new hypothesis was not confirmed by the results of the pathological report which revealed two kinds of tissue; intestinal in the abdomen and broncho-pulmonary in the chest. Two diagnoses where then proposed: complex hamartoma or mediastinal bronchogenic cyst. The pathogenic interpretation in such cases is still very controversial. English authors are prone to classify them as broncho-pulmonary foregut malformations. Macroscopic and microscopic data of the specimen led us to consider our case-report to be a foregut malformation.