Over the past decade, magnetic resonance (MR) imaging has been established as the most widely used examination for the detection of a suspected soft tissue mass and often for depiction of the extent and the characterization of the mass. Sensitivity of the examination for the detection of soft tissue masses is high but specificity is limited. With experience accrued over the past decade, radiologists are increasingly able to predict the histology of lesions based on MR imaging criteria. However, because of the overlap of morphologic features of benign and malignant soft tissue masses, a benign-appearing mass should not be considered benign unless the tumor can be specifically named and its histology predicted by well-established MR imaging features. When a mass is not thought to be an overt sarcoma and there is uncertainty as to whether it is benign or malignant, the tumor should be characterized as indeterminate and approached as a sarcoma until proven otherwise. This article reviews MR imaging in diagnosing and staging soft tissue masses and briefly discusses the radiologistÕs approach to percutaneous biopsy of indeterminate soft tissue masses.