Clinical research on 75 cases of mediastinal masses has been carried out with the aim of evaluating the diagnostic value of Magnetic Resonance (MR). Results which have been achieved point to a remarkable potentiality of MR especially in the characterization and spatial definition of the masses and in the study of the spinal canal. These results, as well as the non-invasivity of the procedure, lead us to consider MR as an investigation of primary importance in the diagnostic assessment of mediastinal pathology.