Radiologists who interpret images of pediatric oncology patients may also be presented with nonneoplastic lesions that bear a clinical or radiographic resemblance to a malignant bone or soft-tissue sarcoma. In these cases, it is often desirable to avoid biopsy. Although not always specific, MR imaging can, in many instances, increase the confidence with which the radiologist is able to rule out malignancy. This article describes the common developmental, infectious, traumatic, and iatrogenic lesions in which the initial presentation is that of a malignant, musculoskeletal neoplasm.