Purpose: to evaluate the role of measurement of ADC value & Dynamic contrast enhanced study in the differentiation between benign and malignant mediastinal lesions. Patients and methods: This study included 70 patients ranging in age from 22 to 82 years with mean age 49.3 +/- 16.85. They were 40 males and 20 females. 40 patients had mediastinal lesions, 20 had lung lesions and 10 had chest wall and pleural lesions. Conclusion: Diffusion weighted MRI and measurement of ADC value are very helpful in the differentiation between benign and malignant mediastinal lesions