Purpose : To evaluate the diagnostic value of magnetic resonance(MR) imaging in the differentiation of benign and malignant soft tissue masses. Materials and Methods: MR examination of 47 patients with pathologically proven soft tissue masses were reviewed. This series included 19 malignant and 28 benign masses of upper and lower extremities, body, and neck. Lesions were evaluated for their margin, signal intensity and homogeneity, pattern and degree of enhancement, involvement of the adjacent tissue, and degree of surrounding edema. Results: Sixteen of benign lesions(57.1%) had well-defined and smooth margin. The tumor margin was irregular in nine lesions(47.4%), however, smooth margin was noted in five cases(26.3%) of malignant lesions. On T2-weighted images, signal inhomogeneity was noted in 84% of malignant lesions and 32% of benign lesions. On Gd-DTPA enhancement study, all malignant lesions(n=18) showed enhancement and 89% showed heterogeneously enhancing pattern. Neurovascular involvement was observed more often in malignancy(n=7) compared to benign lesion(n=1). Direct invasion of the adjacent bone was noted only in malignant lesions(n=3). Surrounding edema was revealed in two benign and 11 malignant lesions. Conclusion: MR imaging appears useful for differentiating malignant and benign lesions by identifying tumor margin, signal homogeneity of tumor, pattern and degree of enhancement, involvement of adjacent tissue, and surrounding edema. The nature of the lesion can be determined in the majority of cases although no unique criterion to differentiate benignancy and malignancy is identified.