Primary tumors of the mediastinum are relatively rare, and benign tumors are about four times as common as themalignant tumors. If the symptoms of a mediastinal tumor have been present for more than one year, the likelihoodis great that the tumor is benign. The differential diagnosis of mediastinal lesions is difficult because of thelarge number of anatomic structures contanined within this small space and the homogeneity of tissue densities.Although numerous diagnostic techniecs may be employed, the location of the tumor still remains the most criticalfactor in arriving at the correct diagnosis. A radiotherapeutic traial is no longer justified in a diagnosis ofmediastinal lymphosarcoma and Hodgkin's disease. If the tumor happens to be an early case of Hodgkin's diseaseswith no other diagnostic manifastation, nothing is lost by a thoracotomy, biopsy, or excision. Adeuqate radicalradiotherapy is then instituted and close follow-up recommended. Here it relates ones on incidence, methods ofstudy and differential diagnosis of mediastinal masses with a review of literature.