When there is a posterior mediastinal mass on a chest X-RAY, a neurogenic tumor is usually evocated. However the occurrence of several other tumors is possible and they should be looked for preoperatively. The literature on the subject is very scarce. We report three cases of uncommon posterior mediastinal tumor. A bronchogenic cyst located between the trachea and the esophagus is described in a two months old girl. The diagnosis is made by tracheoscopy and esophagal contrast study. The anatomic situation explains why even a small tumor induces severe respiratory troubles and requires urgent treatment. An esophageal cyst is described in a 13 year old boy--the mediastinal mass is found incidentally on a routine chest X-RAY because of the risk of complications, the resection of this cyst is required and usually easy when they are intramural. A mediastinal pheochromocytoma is described in a five years old girl. The tumor is discovered during the investigation of a hypertensive syndrome. This location is very uncommon and may be unique or associated with more usual locations. The resection is delicate because of the situation of the tumor in the upper mediastinum. The preoperative angiogram is very helpful in deciding the operative approach.