Experience and problems in the localization, diagnosis and surgical treatment of mediastinal parathyroid tumors are reported. Arteriography, pneumomediastinum and, especially, selective blood withdrawal with assay of parathyroid hormone, have proven valuable to the authors. Scintigram, intravital staining methods and venography are less productive. Retrosternal parathyroid tumors that can be removed from a Kocher incision should not, for practical reasons, be classified with the mediastinal tumors. The authors recommend the one-phase operation. If, after an intensive search of the neck and behind the sternum, no tumor has been found, it is advisable to incise the sternum step by step and revise the anterior mediastinum in the same session.