Over the last half century, our knowledge on germ cell tumors (GCT) has increased dramatically. Tumors that at one time were supposed to originate exclusively from certain anatomic areas are now thought to occur in ubiquitous distribution. Nevertheless, because of their similar histopathologic features, the conventional classic evaluation of these patients will require careful clinical history as well as complete physical and radiologic evaluation. The emphasis in this manuscript will be to highlight the occurrence and overall characteristics of one of the most common GCTs in the mediastinal region—seminoma. A more detailed discussion of mediastinal GCTs is well beyond the scope of this review.