Metastatic tumors from extrathoracic sources appear in the mediastinum infrequently and from a variety of locations. In this series of approximately 350 malignancies of the mediastinum, 20 (6%) originated from the breast, prostate, kidney, pelvis, and gastrointestinal tract. A radiologic review of these cases does not identify a unique pattern, although paratracheal masses present most often, while unilateral hilar adenopathy occurs somewhat less frequently. The history of previous surgery for malignancy suggests metastatic disease into the mediastinum. However, other entities of second primaries, lymphoma, Hodgkin's disease, and benign processes warrant consideration. Mediastinoscopy is reemphasized as a valuable diagnostic technique for the solution of these problems.