Germ-cell tumors occurring primarily in the mediastinum have been well recognized in the literature for many years. Unfortunately, most of what has been written on these tumors has been in the form of case reports and small series of cases, thus precluding a better understanding of their clinical and demographic features, as well as of their biologic behavior in this particular location. In addition, mediastinal germ-cell tumors not only have never had a standardized nomenclature, but they also have lacked the benefit of a clinical staging scheme for assessment of prognosis. Another important aspect of these tumors that has required attention is the frequency with which teratomatous lesions are associated with malignant components in the mediastinum. Comprehensive studies of mediastinal germ-cell tumors to determine whether these lesions recapitulate the distribution, histopathologic features, and biologic behavior of their counterparts in other areas, such as the gonads, have been lacking for many years. In this article, we review our experience with a large series of cases of primary mediastinal germ cell tumors and examine recent concepts and advances in our understanding of these unusual and diagnostically challenging neoplasms.