Of the many types of tumors located in the mediastinal compartments, most are metastatic. The most common adult tumor in the anterior compartment is thymoma. A number of important cytogenetic, immunohistochemical, and molecular analytical observations have been reported over the past year regarding this tumor. In addition, reports on the multimodality management of thymoma have raised important issues regarding the prognostic significance of selected pretreatment parameters. Of special interest are reports which may clarify differences which may exist between thymic carcinoma, a separate pathologic entity, and thymoma. Finally, important observations regarding the association of hematologic malignancies with germ cell tumors of the mediastinum have been made in the past year. The following review summarizes pertinent progress in the above-mentioned areas and cites interesting reports pertaining to less common mediastinal tumors of the posterior and middle mediastinum.