The results of the CT-investigations of the mediastinum on 500 patients can be described in the following way: the assessment of mediastinal lymph nodes was clearly improved by the CT. About half the positive mediastinal findings in malignant lymphomas was to be proved only in the CT. The diagnostics of mediastinal space-occupations was elevated to a higher degree. Statements concerning the coarse tissue are possible. In myasthenia gravis pseudoparalytica the computed tomography is the best method for demonstrating the morphologic relations. The individual changes of the thymus gland are, however, not certainly to be differentiated from each other. Among the vascular changes aneurysms and an arcus aortae dexter with right descending thoracic aorta can unequivocally be demonstrated. A particular advantage of the computer tomography consists in the possibility to separate the perfused lumen from the thrombotically closed one. The search for a primary tumour in the mediastinum is not useful in negative conventionally radiographic findings.